I haven't done the math, but just eyeballing it from following the topic closely so far, it's looking like the best mix of games is Smash 2v2 w/ Limited Items, MvsC2, and Tekken 6. While no Melty Blood or BlazBlue makes my inner weeaboo sad, I'm good with these games too.
It seems like they strike a decent mix of
-flashy (MvC2 is frantic is nothing else, and T6 has a lot of really hilarious abilities),
-multiple genres (2D/3D/Platform fighter),
-familiarity (people know Smash and Capcom, and even Marvel/Tekken to some degree),
-serious competitive ability/accessability (T6 is well-balanced and not enough people are experts at it for the skill gap to be a big problem, Smash 2v2 and MvC2 are easy to pick-up and play even if the balance isn't as great),
-availability (MvC2 is PS2 at least, and Gamecube controller availability is the biggest hurdle to Smash)
-time (MC has pointed out that Smash 2v2 and T6 have some pretty quick matches)
-novelty (we've never done Smash team matches before and MvsC2 is too classic to never be one of our tournament options. Tekken as a series hasn't gotten a showing yet, either? Also, T6 is brand-spanking-new in the states, right?)
-lack of hate (well, I haven't seen anyone really roast these titles like NEB's disdain for BB, so I'm assuming most people are open to giving them a shot)
Keeping it to just three games keeps the length down, too, and personally I'd -really- prefer to get it all done in one day. There will be plenty of fighting games at the con anyway, we don't need to devote more than one day's group-time to them.