Actually, I think I will comment on everything suggested in this topic, just for the hell of it, while I'm here.
SF4: Worked out fairly well. Wouldn't hurt to have again.
Tekken 6: Mash friendly, fairly fast, fairly decent looking. Downside is that no one here has any fucking clue about 3D fighters, but that didn't keep Soul Cal from being fun.
Melty: Too combo intensive to prevent anger, based on BB reactions, and we have too good of a base at AC-this would end up unbalanced as hell, as most(not nearly all, but far too much) of AC carries over to AA.
TvsC: No one has any clue how to play this and it involves a guy putting a Servbot helmet on someone and punching him through zombies as one of the super options in the game. Pretty good chance this would pan out pretty well.
KoFXII: Not too bad, we have people that know KoF in general but as I understand it 12 is different enough to prevent too awful much of that from carrying over. Would work, though people might get frustrated, since it's closer to the technical end then not. Still, not hideously or anything, it's not Guilty Gear.
Blazblue: People bitching too much obviously means it's bad, even though it appears to be a minority. We have a skill gap anyways.
Smash: No 64, it is the sort of game that appeals far more to people that are stupidly into Smash then not. I like 64 mind you, played it a while, it is fun. No 64. No Brawl+, same thing, even assuming the hack is excellent-which I am not certain on, having heard many things about it that make me iffy on it at points, though sadly I cannot recall them.
Both are going to be rewarding the people already best at Smash. This is a terrible idea, as this is one of the few fighting game series we are into, but there's not a universal into it here. We don't want the gap between casual players and serious ones to become even worse. Smash is a game where the fact that we like it mitigates some of it's problems, but those problems don't need to be larger.
I highly suggest 2vs2 team tournaments of either Brawl or Melee. This levels the playing field hilariously, allows items to be more balanced(As the law of averages shows, 50-50 chances are more balanced in practice if you get more of them. "Object appearing closer to me then them" is a 50-50 chance. You have more people it can appear closer to and more raw life that it can appear closer in. Simple.) and in general is way funnier.
MvsC2: Worse then TvsC for this group. (...actually just worse then TvsC in general unless you're really into infinites and ridiculously long combos, from what I've watched up on it.)
Dissidia: What Meeple said. Bad game for a bunch of people to pick up and play. We also have the same kind of internal skill gap BB has.
For previous DLCs, the games that stood out most either way were VF and SO3(negative) and Fantasia(Positive). Battle Fantasia feels like a one-off but it seems like we can successfully rule out subgames ala, well, Zone of the Enders, based on SO3's reception. If you can think of a fighting game subgame to another game that you actually found good enough for a tournament(You being anyone here), I would like to hear it because I'm not able to think of one. VF reception rules out VF forever, we're not a VF crowd.
Some other things to note: SF2 generally was received decently...and has a newer upgrade in SF2HD, which has enough subtle changes to rub out "Good person who really knows the game instantly wins over anyone" and has enough better graphics to be more fun to watch. As an added benefit, it's one of the simpler fighting games.
Non-fighting games I'm really blanking on something simple enough. I mean KDC would be fucking awesome but sadly that *is* something where it is simply way, way too long. I dunno. Anything RPG-based isn't going to work out, likely, either. Dunno.