Charisma, and anyone who's worked in the corporate world would know why. That stat trumps all others.
Strength? Eh, you'd just get asked to help people move furniture a lot. Charisma will help you talk others into helping you.
Dexterity will make me a better driver I guess, but a high charisma means I'll always be able to talk someone else into driving, as well as guarantee I ride shotgun.
Constitution might be nice with a high Charisma, what with the STD factor and all (oh, and all the people who said a high CON will help them live longer, remember that in D&D lifespan is a random roll and a high CON won't help you).
Intelligence? Look, most people in the world today are a 10 or 11 (well, maybe lower), so it stands that most D&D players are too. I'm gonna go off on a rant here, but all you people who claim to be 14 or 15 INT are lying to yourselves. Real people with INTs that high are too busy constructing macroeconomic models on petroleum futures for the Rand Corporation or teaching supercomputers how to beat Bobby Fischer to play an RPG. Even an uber-nerd like Bill Gates isn't even an 18. You think it was a high INT score that let him talk IBM into that DOS contract? Pure CHA baby, haircut notwithstanding.
Wisdom is everyone's drop stat. Wisdom's overrated. I'd never have done half the cool, fun, off-the-wall crap I've done in my life if I'd been wise enough to know better at the time. Besides, millions of people listen to Dr. Laura for advice everyday, and she's about as wise as swimming during a thunderstorm.