Ok, so here are more details on my games.

On Total War scenarios, victory conditions are hard to achieve with few activations. And Most of my formations are easy to break.
For exemple, the Revenants were broken most time.
About the firepower of the titans, I admit I wasn't that lucky ... And they killed few targets.

On my 4th games, I was oppsed to a Gargant Mob : 1 Great Gargant + 5 Kustom Gargants, with 8-12 BP ... This is a really special configuration, but I give up as I totally lack firepower to get through Energetik Field and damage a Gargant without exposing my titan to a Gargant Assault. In return, the Gargants were unable to kill my titan (holosield + high 'to hit' value), but broke them sooo easily.

I played the Tournament scenario game against a new player who split too much its Space Marine army, so I finally achieved to win !

Last game : a Megageddon : 2 teams (Eldar vs Chaos) of 3 players with 3000ts armies. I did pretty well, but only because my direct opponent fears the backup of my 2 allies.

These were my first games with the ETC, so I made some placement mistakes.
I was also thinking about 3 activations ... but I realised I've got no Farseer !
ETC is not like AMTL ... So I have to adapt.

About Farseer (not to say about assaulting), it's a pity that the Warlock titan seems so essential. The Phantoms should be the backbone of the list.

Here is a proposition for the pulsar:
75cm 2*MW3+ TK(1)
or
60cm (or 75cm) 4*AP3+/AT3+

Brilliant summary post – thanks very much. I've added my thoughts on how your individual points relate to my experience of the Eldar Titan Clan in playtesting. For the most part, I'm simply putting my thoughts down, without suggestions for changes, so Angel_of_Caliban can make the hard decisions.

Specialisms
Eldar Titans seem fairly specialised at taking out War Engines. This is fine in the Biel Tan list, but my regular opponent struggles to place useful damage on my multiple infantry formations (since the shots often kill Rhinos etc rather than damage-dealing units). This can be ameliorated by taking non-Titan formations, but that starts to dilute the theme of Titans. I would be interested to see how the Eldar Titan Clan (ETC) works against a horde-style army like certain builds of Guard, Tyranids or Orks.


Command and Control
In contrast to Biel Tan lists, the ETC command and control is extremely reliable. It's been very rare for my opponent to fail a command check, even when broken; as the Titans can generally flee 70cm, will rally on a 3+ even if I can get a formation near them, and generally have a re-roll thanks to a very survivable Supreme Commander. It's also impossible to supress the Titans themselves without breaking them; so where you can spread a few blast markers around Biel Tan and have some significant disruptive effect, the exact opposite it true of the ETC.


Durability
The ETC takes Rug's point to extremes – the Titans are hugely resilient at every range, but getting crossfire causes big problems for them, and their numbers are even smaller than Biel Tan, exacerbating the problem. Basically, every one of Rug's points in this category is doubly applicable here.

Lack of Garrison Options[i/]
The ETC as a whole seems low to mid-ranged, with few 'reach-out-and-touch-them' options. Rangers are the only option for ETC (right?).


[i]Mobility
Equally true of ETC as Biel Tan.

Skimmers!
While the specifics aren't the same, Eldar Titans rarely struggle to draw LoS. CC isn't impossible for the enemy – but Eldar Titans are bloody good at it!

Fire power!
While the firepower is there, it's more focussed than in Biel Tan, and there's less of it. To balance this, the ETC generally won't struggle to activate theirs.

Assault power!
ETC have it in spades. In fact, I think this is their greatest strength.

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Industrious, red-robe wearing member of the PCRC

I always feel fun about this : the standard rule is there is no limitation on fire arcs.
It's not because imperial and orks big walkers have limited arcs that a special rule must be introduced to say that eldars titans follow the standard rules !

That's fair enough. If Angel_Of-Caliban wants to keep it, I'd suggest removing it from every Titan's notes and just put it at the start of the list as an aide-mémoire:


+++

Well, most armies will find achieving certain victory conditions easy and some hard in that scenario. Any War Engine-heavy army should find it very easy to prevent the enemy getting Hold The Line, and a concerted drive should snag them the Blitzkrieg, setting you up for a Take and Hold. The weight on concentrated firepower should generally mean they find it easier than a 'normal' army to get Break Their Spirit.

Conversely, they're at higher risk of Break Their Spirit than a lot of armies, will struggle to prevent Hold the Line themselves, and if they're too aggressive, they'll leave all of their hom objectives free.

Swings and roundabouts, I think.

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Industrious, red-robe wearing member of the PCRC

It's not a special rule, it's a reminder. I got no problem imagining countless groups (not active on the interwebz) houseruling fire arcs in because "all other titans have it, it's clearly a typo".

Four. They have leader.

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Currently doing a plastic scenery kickstarter

The pairs do not, correcto.

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Currently doing a plastic scenery kickstarter

As the blue wolf says, they have leader which goes some way to ameliorating this problem. It's quite demoralising as the opponent to see the broken titan pretty much back to where it began on a successful rally – but that's a good thing! I like the 'elite' feel of the Eldar titans.



This has certainly been the case in our test games. It ought to be noted that Bob_Hunk and I really like to ensure that War Engine lists 'max-out' the Titans, so we're often low on support in comparison to the other lists we see online.



One of the things I've noticed is that ETC lists suffer doubly from low numbers thanks to their expense (low activation count) and Farsight (if they use this, they compound the problem):

This tends to result either in the ETC player not using Farsight (so as to minimise the potential for opponent's late-turn flanking/objective grabbing etc); or ceding large numbers of late-turn activations to the opponent. Using Bob_Hunk's and my lists from earlier, and assuming he retained as much as possible, it's entirely possible that I would have half-a-dozen or more activations after he's completely finished: a huge tactical disadvantage for him.

I wonder if something other than Farsight could be playtested to ameliorate this (some way of 'skipping' activations, perhaps?); or a points-break being given as Farsight is less useful in a War Engine-heavy list?

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Industrious, red-robe wearing member of the PCRC

(My emphasis)

Yes, I'd agree – the other War Engine lists (AMTL and OGBM) have sturdy, resilient formations; both as the main Titan/Gargants and their supporting forces. Neither is true of Eldar.

Being continually out-activated seems quite 'un-eldar' to me, too – it's as though they're being continually outthought. Riffing on my suggestion above;

... I'd quite like to playtest something that let the eldar have bonus activations for each Phantom Titan as outline below:
e.g.

Army list: Two Phantom Titans (A and B) and a Warlock Titan (C).
Enemy list: Seven formations (X, Y, Z, M, N, O and P)
Enemy win strategy roll.
Enemy Activation 1: Enemy formation X doubles forward.
Eldar Activation 1: Phantom Titan A activates and shoots the enemy formation X.
Enemy Activation 2: Enemy formation Y advances
Eldar Activation 2: Phantom Titan A 'ghosts' – Nothing happens.
Enemy Activation 3: Enemy formation Z doubles forward.
Eldar Activation 3: Phantom Titan B 'ghosts'.
Enemy Activation 4: Enemy formation M sets overwatch.
Eldar Activation 4: Warlock Titan (C) advances and shoots Enemy formation X.
Enemy Activation 5: Enemy formation N marches.
Eldar Activation 5: Phantom Titan B advances and shoots Enemy formation N.
Enemy Activation 6: Enemy formation O doubles.
Enemy Activation 7: Enemy formation P doubles.
END OF TURN

Replacing the Farsight rule with the Grasping At Shadows rule (or whatever you'd like to call it) means:
1) The Eldar regain some Eldar-like flexibility.
2) Reduces their very reliable Command & Control somewhat (Farsight and 1+ initiative is a deadly combo, particularly on such reliable platforms) and restores a traditional Eldar weakness.
3) Ameliorates the activation advantage in an Eldary way.
4) Gives the Phantom a minor boost in a specialised list.
5) Keeps both players involved in the game throughout the turn.
6) Doesn't completely eliminate the problem of low activation count.

Thoughts?

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Industrious, red-robe wearing member of the PCRC

I think we have a fundamental difference in opinion, them. I can make a two Titan list with a 4500pt normal force - the ETC list, in my opinion, should allow lots of titans. Otherwise, what's the point?

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Industrious, red-robe wearing member of the PCRC

Personally, I think no list should be able to be only titans. That's an entirely different game, something like Battletech or Adeptus Titanicus.