I don't think there's a specific guide to titans, but a quick summary.

First of all, all titans require the same XP to level up. You get XP from blowing ships up while your titan is in the gravity well. The XP will be split among all capitalships and titans owned by hostile players to the owner of the destroyed ship.

The main differences are in the abilities, which I'll summarize below.

1. Ankylon: Hardest titan to kill, has a good self heal, especially in friendly gravity wells. Can also make its fleet much tougher to kill and disable abilities while doing Area of Effect damage (AoE) to a large number of targets. It doesn't match the fleet destruction capacity of a lot of other titans however, so it can be slower to level up. The TEC loyalists do get an XP bonus tech though that applies in your own gravity wells.

2. Ragnarov: This thing is a beast, thats really the only way I know how to put it. It has two unlimited target AoE attacks, and snipe gives it to put a lot of damage on a single target. Its ultimate Overcharge can double the effectiveness of these abilities for a small antimatter cost too. That said, you'll quickly run into antimatter issues if you try to use all these abilities at once. Still probably the best titan for beginners though.

3. Coronata: Its actually one of the best things the Advent Loyalists have. Unity Mass is a bit lackluster compared to snipe. However, Subjugation aura is a great passive ability that will seriously reduce enemy damage. Subjugating assault meanwhile allows the Coronata to have a chance to capture any frigate its weapons damage, making it a good emergency source of reinforcements (or for collecting a fleet of doom well above the fleet supply limits). Repossession makes sieges much, much faster as you can instantly capture a planet.

4. Eradica: Probably one of the most feared titans. Chastic Burst maybe the best titan ability in the game, it can target it any direction and does tons of AoE damage. It can also sacrifice a friendly frigate to gain its shields, hull and antimatter, giving it a potentially very powerful heal, especially if you use guardians. It also has a passive that will increase its weapon damage for each friendly ship that dies near it, giving it a great synergy with all the other Advent Rebels on death bonuses. As for its ultimate... its pretty well hated. If you are facing a good player he will run when the titan dies to prevent the 4 minutes of god mode you'll get. However, if they can't run or don't realize they need to, you'll quickly kill anything your titan catches up to.

5. Vorastra: Probably the weakest titan starting out. Its main use is spawning phase jump inhibitors to ensure a Vasari Loyalist fleet can be extremely mobile while destroying planets with striped to the core. It can also jump in the gravity well to quickly get out of danger, and has a unique passive ability called Subversion that increases its defense, gives it splash damage and can greatly increase its rate of fire while taking damage. However, the real fun is when you get to level 6. Once you get maw, this thing can literally eat up frigates as good as a Ragnarov or Eradica, and with micro phase jump there is no where for them to hide.

6. Kultorask: While not relying on brute force as much as the Eradica or Ragnarov, the Kultorask is still incredibly dangerous for frigate groups. With nanoleach it can drain them of hull and antimatter while the Kultorask gains it, making it almost invincible if your opponent brings large numbers of frigates. It can also disable these frigates, preventing them from escaping, and heal its own fleet. That said, none of its abilities affect capitalships or titans, so you'll need a large group of frigate support yourself, or even better the Vasari Rebels phase jumping starbase (AKA "Orkulus Rex", sometimes called the 7th titan).

I don't know if there are any guides to them but i'll try to explain them from my experience.

This is not very extensive, but I hope it helps!

1. Vasari rebels: Kultorask Titan

This is an excelent Titan that does not do a lot of damage but is hard to kill.

Strategy:

Couple it with a jumping Orkulus for dps (adding a  Jarrasul Evacuator to this combo is something I like to do for its Nano Disassembler). Nano Leech is the skill you want to invest in as that is what makes this titan so scary.

Important: When fighting this Titan, avoid going against this Titan with a large fleet as its Nano Leech ability will leech off the fleet and keep it alive. The larger the fleet, the more it steals.

Abilities:

1. Nano leech 

Using this ability the Kultorask steals Hull and Antimatter points from the opponents fleet. More number of enemy ships, the higher the heal until its cap.

2. Nano Remit

The Titan sacrifices some Hull and Antimatter to heal its surrounding fleet.

3. Gravity pulse

If the enemy ships are under the influence of Nano Leech then this ability diables them.

If the enemy ships are not under the influence of Nano Leech then this ability slows them down and increases the time for their weapons to cooldown effectively reducing their dps.

4. Dissever

Does damage to nearby enemy ships and the damage is higher if the ships are under the influence of Nano Leech.

2.Vasari Loyalists: Vorastra Titan

This is one of my favorite Titans after its buff. Very versatile Titan, has decent offensive capability(after phase missiles and wave type damage were incorporated) but is a tad weak compared to other titans until it reaches level 6, and has an excellent initiation/escape skill.

Strategy:

You only need one point each in Deploy Phase Stabilizer and Micro Phase Jump earlier on and so concentrate the skills points into Desperation and upgrades to increase its tankiness. Micro Phase jump can be used to escape if need be. At level 6 take The Maw skill and this is where this Titan becomes truly deadly. Use the Micro Phase Jump to close the gap to the enemies fleet and use The Maw and watch as their fleet disappears . If it reaches level 10 usually my Vorastra would have The Maw and Desperation abilities maxed out as well as the armor and weapon upgrades. One point in Spawn phase stabilizer and the rest of the points into the Micro Phase Jump so the the Titan can jump farther.

Important: Get this to level 6 as soon as possible for its excellent skill, The Maw.

Abilities:

1.Micro Phase Jump

The Titan teleports a distance. The higher the skill the further its can jump.

2. Desperation

Excellent skill. This skill negates some of the damage it takes increasing its tankiness. The Titan gets splash damage and while the titan is dealt damage its dps increases.

3. Deploy Phase Stabilizer

Spawns a phase stabilizer in the gravity well that it occupies, this includes enemy gravity wells also. Excellent for mobility. I honestly have not had the need for more than one point in this skill.

4. The Maw

Excellent fleet killing skill. The Titan sucks in ships in a cone shaped area right in front of it, so for its maximum effect make sure its very close to the opponents fleet so that the enemies ships are in range. Avoid having this skill on Auto-cast as the cool-down is quite large. You get resources for the sips that get sucked in and the titan now gets exp for the ships sucked in.

3. Advent Rebels: Eradica Titan

With a few levels this titan is very dangerous and hard to kill although its somewhat fragile earlier on. It is skill dependent. It is fleet dependent to obtain its full efficiency. This Titan, after getting the required skills, does a lot of damage.

Strategy:

Which abilities to choose and when is somewhat situational so choose whatever skills you need the most at the time without leaving out the other skills entirely. Chastic Burst is always a good choice as it is a fleet killer and it has a low cool down. Invest in Purification especially if you are going against a difficult opponent as this will keep your titan alive longer though at the expense of a few frigates and Strength of the Fallen is also excellent in this scenario as a difficult opponent is going to be killing your ships and this will in turn increase the dps of the titan. Having Unyielding Will can turn the tide of a battle.

Abilities:

1.Purification

Destroys one of your own frigates or cruisers and it absorbs the remaining hull, shield and antimatter. This skill is an excellent heal that makes this titan hard to kill but it feeds on its own fleet. Kinda cannibalistic if you ask me

2.Chastic Burst

Damages an area around a target. This is an excellent AOE fleet killing skill and it has a relatively low cooldown. Does a ton of damage.

3.Strength of the Fallen

The titans dps is increased when friendly ships are destroyed around the titan. This effect stacks for each ship destroyed. Nice skill that increases the damage it does when your own fleet is dying.

4.Unyielding Will

When this Titans hull is depleted it becomes invulnerable and goes into a omg wtf crazy state. It gets boosted ability cooldown and antimatter restoration rates so you it can use abilities like crazy. If you are in the opposing side and the opponents Eradica reaches this state, stay away from it.

4. Advent Loyalists: Coronata Titan

A great Titan. In an ideal situation this thing is a beast but if you go against one you can deal with it with a carrier spam as its suppression aura doesn't affect strike craft.  It is also fleet and tech dependent for its dps.

Strategy:

Concentrate putting points into Suppression Aura and Subjugating assault as both of these are going to help you immensely. Buff the titan up with armor upgrades and choose weapon upgrades if you like. Take one point in Repossession when the Titan reaches level 6. Dump the rest of the points into Unity Mass is you want a nuke that does decent damage.

In fleet battles you will want to turn Subjugating Assault on Auto-Cast so that you steal their units, thus reducing their fleet strength and increasing your own. Make sure your Titan is in the midst of the battle so that the enemy units are within the range of the Suppression Aura. Use Unity Mass only when required as your antimatter usage should be focused on Subjugating Assault.

Note: The Suppression Aura doesn't affect strike craft.

Abilities:

1.Subjugating assault

This is an excellent skill, when it is active it reduces the Coronata's dps but has a pretty high chance to capture enemy ships through its weapon attacks. In the last game I played on a medium to large map against hard AI, by the end of the game half the fleet I had was captured units this skill captured. This skill is economical in a way as you don't need to build as many ships as you capture the rest.

2.Suppression Aura

This is another amazing skill as it reduces the dps of all enemy ships and structures within the area of the aura. It also slows down the enemy ships making it difficult for them to run. This skill is always useful. Especially useful in fleet battles and when assailing starbases. Its important to note that this skill doesn't affect strikecraft.

3.Unity Mass

This does damage to a single target according to the number of friendly ships around the titan. There is a cap on the amount of ships the damage takes into account. This skill is not as great as the other skills and thus the other skills should have higher priority over this one. I personally wish this skill was reworked.

4.Repossession

The ultimate sieging ability. When this is used against an enemy planet you immediately gain possession of the planet. This is an excellent skill to reduce time in capturing a planet and it has offensive uses too as since you capture the planet,  the enemy wont be able to create ships from their frigate factories present at the planet. Honestly only one point in this ability is required.

5. Tec Rebels: Ragnarov Titan

This is the best 1vs1 Titan in the game. It packs quite a punch. It is decent vs fleets.

Strategy

This Titan does an immense amount of damage. Concentrate on Snipe and Scattershot first before the other skills. The other skills are not as important as you will want to save antimatter for Snipe as it takes out the high priority targets the enemy has. Overcharge greatly increases the damage of the other skills, for a moderate antimatter cost, so keep this in mind. Use explosive shot together with the other skills to bring down targets faster and to disrupt enemy formations by pushing them back but do so when you have the antimatter to do so. Enjoy the carnage

Abilities:

1.Scattershot

Does damage and reduces armor to enemy ships in a cone in front of the Titan. Excellent ability to use against enemy fleets. The amount of damage dealt is increased if the Titan is under the effect of overcharge.

2.Snipe.

Excellent ability to use against single targets that have high hull(capital ships, starbases and titans). It has a very low cool down time so it can be used many times in a battle. Overcharge increases the damage down by Snipe.

3.Explosive Shot

It deals damage and knocks back nearby ships. Does more damage with Overcharge.

4.Overcharge

When this is used, it increases the effectiveness of the other skills. You may not wan't to use this if you are low on antimatter, in such a case use the other skills instead.

6. Tec Loyalist: Ankylon Titan

This Titan is extremely oriented towards defense and fleet support. It is hard to kill. It gets bonuses in its own gravity wells which makes it extremely tough to take down. Its Group Shield ability is an excellent support skill.

Strategy:

This Titan is much more effective in a gravity well that it owns so keep that in mind. Earlier on, one point in Disruption Matrix will do for the disrupt and concentrate in Group shield as this will help keep the fleet surrounding the Titan alive. Put points into Furious Defense to increase the dps it does as well as its durability. Take Inspire and Impair when you can. 

Abilities:

1.Disruption Matrix

This ability does damage over time to enemy ships and prevents them from using abilities for a short time in an area around the Titan. Should be great for interrupting skills like an enemy missile barrage or to prevent an enemy from interrupting yours.

2.Furious Defense

When used it repairs the Ankylon for the duration of the skill and increases its damage output. How much it heals and the amount of damage done is greatly increased when the Titan is in one of its own gravity wells. This skill is one of the reasons this titan is hard to kill.

3.Group Shield

This ability reduces the damage friendly units take. This ability is an excellent fleet support ability and makes the surrounding friendly fleet much more durable.

4.Inspire and Impair

This is another excellent support ability which increases the damage dealt by friendly units by reducing the cool down time of their weapons and this ability also increases the cool down time of the weapons on enemy ships thus reducing the damage they deal. This ability affects the entire gravity well but has no effect on Titans.

......Phew, that took some time!