MS has good online.. but theyre single player is often rubbish
Sony has okay online.. but the most online played games are likely to be multiplatform.. Single player is very often top notch (Uncharted 2, Heavy Rain, GOW3)
Nintendo are the masters of replayability.. in sheer fun they are IMO undefeaten (although LBP is in that league) but in online they simply don't come close to the competition
conclusion:
If you feel like having a night of gaming, the Xbox 360 offers you a nice night of online Halo 3 or MW2
If you wan't something to spice up your parties, the Wii is all you need. It has alot of games that will keep your friends laughing
PS3 is something of all.. it has TOP NOTCH single player games, decent multiplayer (although likely not enough to have you going all night) and it has its fair share of party games (buzz, singstar, LBP)
Currently playing: MAG, Heavy Rain, Infamous
Getting Plat trophies for: Heavy Rain, Infamous, RE5, Burnout and GOW collection once I get it.
