Imperial fists are cool and all, but Yea. The damned game is named after the Templar Flagship/Sigismund's vow to prove his chapters loyalty to the emperor.

I'm just puzzled as to why the Black Templar wasn't the FIRST chapter they selected when the game is called Eternal Crusade. That phrase is as Black Templar specific as "We march for Macragge" is for Ultramarines. If the game was called "Blood for the Blood God!" the first faction I would think would be World Eaters or Khorne more generally.

It just seems odd to me.

At any rate, the more the merrier, right?

I obviously can't tell you exactly why they have a large following, but I can tell you why I like them and safely assume that a chunk of those ppl like them for similar reasons.

There's the obvious things like knightly demeanor, look, and practices, the color scheme the affinity for cc. I like them for those reasons as well as most but also because I love the shit out of Dorn. I love the absolutely ridiculous amount of zeal that they have for the Emperor and continuing the Great Crusade. Made all the better by the fact that they don't worship him, but still maintain the fanaticism (this will depend on what lore you view as more authoritative canon. More thorough fluff comes out from Black Library than the codices, so I trust the novels more. And the novels say they don't worship him.). I love how they couldn't give less of a fuck about the organizational instructions within the Codex Astartes.

But the main points of all these for me are the knightly aspect, penchant for cc, and devotion to the Emperor. I've always thought knights were cool, from their armour to the chivalry and way they do battle. Close combat has forever been the more personal form of combat which is why I prefer that. But the zeal is the real selling part for me. The unwavering dedication to the Master of Mankind and all that he strove for(and will strive for again once he returns from near-death...ahem). A belief in the cause that they fight for is the coolest thing about any soldier to me, and while most chapters have any combination of these things, I find the Black Templars to be the most potent concoction for me. I mean they're close to being as faithful as the Grey Knights are, and they don't even worship him like the Grey Knights do. Hope that helps.

The key word there being "IF" if all SM's are equally good at everything, then there is no discussion here, our choices are based on aesthetic value alone.

"IF" however, each chapter is going to, in some way, capitalize on their chapters' tactics, then we have a discussion. While the BT's may be the most zealous of the chapters (not sure that is accurate, for the sake of argument lets say it is) they bring nothing to the table that is not already there.

Now the Iron Fists, Raven Guard, White Scars, etc all bring different specialties beyond just being able to mix it up with a cool paint scheme on their armor.

Now before you start a poll to see if I should be thrown to the warp, keep in mind I like the BT's I think they are an awesome chapter, I love their parent chapter, I have nothing against the BT's (or any chapter for that matter) other than they specialize in up close and personal combat like several other chapters, one of the most notorious of which is already in game.

So I love ya, I do, and later in the game I will support fully having the BT's in, but not at launch. This is all based on "IF" of course.

Given that the Iron Warriors are confirmed for Chaos, then my choice would be the Imperial Fists to act as a counter point in terms of tactics. Also, I think in the early stages of the game's life, I think it's more fitting to stick with First Founding chapters, from this point you could bring in successors (Crimson Fists, Black Templars etc as DLC).
As for the Grey Knights, it's a bit tricky in terms of the mechanics that have been announced. Without the inclusion of demons or psychic powers/weapons any form of the Grey Knights would be unnecessary/ seriously under powered or very sketchy lore wise. As previously mentioned, the whole secrecy/legend angle would be diluted if you had thousands of Grey Knights running around.
It would be a cool future project to see psychic powers, force weapons and a full range of demons included in the game, especially a demon prince progression option for Chaos which could then be countered by a Grey Knight option for Space marines.
P.S. Kernowstig is right, we have a solid, active community on PS3. Seeing as you can pick up the game for buttons,it's well worth checking out. The intention is to keep going and use the site to bridge over to the EC community once the game is out.

When were they confirmed? Please point me at those facts!

In the very beginning, the two chapters announced were Dark Angels and Iron Warriors as far as I can remember.

No Chaos Marines have been confirmed, that I can find.

In a picture of game fotage from I believe was comicon you can see the iron warriors symbol on the walls of the fortress