My 7 year old daughter would tell you to get a PS3. Little Big Planet is her killer app, and she prefers the controllers as the 360's are a bit chunky for her.
I prefer the PS3 as well because I like their exclusive titles over 360's. I don't play online much (I use a PC for that) so maybe that colors my preference, but you know when I DO play online, it works flawlessly and I have a blast pwning fools in BlackOps so I don't know why Sony gets slagged on so much there (even before THE INCIDENT).
My 15 year old son, of course, would rather die than give up his 360.