I'd say the Xbox interface/dashboard is much more user friendly and, if i might add, more dumbed down. Their newest dashboard update is pretty nice and sleek though.
However in almost every instance, I found PS3 exclusives better. One major flaw though is that not that many people have mics on PS3 compared to Xbox. While this is not always the case for some people, I myself like to talk to people and not have a silent game-room.
But I find a lot more mature players on PS3 than on Xbox.
Another thing is party chat. Sure, you can talk to your friends while playing different games but seriously there's no need to do that at all and I think that's dumb. If you're playing a game, you should focus on that. If you want to host a talking party, call them on your cell phone or something.