Data would be an endless source of party fun.
1) Jokes delivered in strange, endearing ways
2) Attempts to hit on women hilarious and odd
3) Beat ur ayss at poker (or any other game)
4) Could act out a scene (complete with voices) from any play, by request
In fact, the only one who might be better at a party (if he could improve his sense of whimsy) would be Odo from DS9. Data can't shapeshift!