I think one thing that's important to me as to which machine is the better choice is in its multiplayer/online capabilities. Me and my mates have gaming nights every 2nd weekend and we have access to all 3 machines. Of the group of 5, 4 of us have a PS3, one has an XBOX 360 and one has a Wii. We only play the XBOX 360 occassionally - one night we were playing Gears of War but after 30 minutes of gametime, the machine bricked on us (it has since been replaced under warranty). The Wii is a greaty party machine but we don't play it that often as we find the games too gimmicky and too kiddy. The PS3 gets the most playtime because of its online capabilities - we play Warhawk, Tekken, Mortal Kombat and Ridge Racer Online all the time and it never gets boring. Even when we don't have game nights we stay at home and challenge each other online from the comfort of our own homes. The XBOX has online capabilities too but none of us wanna risk buying one since that bricking incident. The Wii just doesn't offer a true multiplayer experience unless you are all together in the same room and it hardly has any games you can play online. So it comes down to this:

PS3 - decent games, best machine to play online
XBOX 360 - good games and online functions ruined by reliability issues
Wii - great party machine, almost non-existent online games to play

So for me, the choice is easy - PS3.