SSBB all the way, even GTA4 combined sales won't beat it.

I'm thinking GTAIV, but only because it's on two platforms.

-edit-

So had it because like a weekly thing for this thread to be made? 

SSBB>Either platform GTAIV
GTAIV both platforms>SSBB

GTAIV, I prefer beating on seniors, running people over, and slaughtering the police/SWAT/Special Forces over beating the crap out of Nintendo and friends' videogame stars. But only by a small margin.

I'm giving the very slight edge to GTA, at least for the first year or two. GTA games have good legs, but, for comparison, Melee kept on selling from the GC launch right up until very recently (and it still sells at a decent clip, considering it's on a dead console, is 5 years old, and its' sequel comes out next month)

Tifa, its about sales not preferences.

I am going to cop out:

Both.

BRAWL FTW

@Tifa: apparently you didn't read the OP. He asked which you think would sell better, not which you like more.

 I tried to sell my copy of SSBM at Gamestop a month or two ago and the clerk looked at me like I had just choked a baby.  It still actually fetches a nice price (though I didn't sell it, he convinced me not to).