I have both but I'm not sure what you mean by "slimmed down". I prefer the XMB to the NXE but viewing and comparing friends profiles is quicker on the 360. I find that PSN and Live both have their advantages-
PSN has more dedicated servers than Live, I think every 1st/2nd party Sony game has them. Resistance 2 with 60 players and no lag and Warhawk are simply head and shoulders above anything I've played on the 360. And the PS Store has no file size limit so you can download large games like Siren, SOCOM, Warhawk etc. And Remote Play is an awesome feature.
Whereas Live has better chat features and the advantage of cross game invites. So it's easier to set up a game with friends at the moment. And I like how updates are quicker on the 360, they do take longer on the PS3.
But at this point, if I had to choose one service it would be the free PSN. All I think Sony REALLY need to do now is cross-game voice chat. Having barely any dedicated servers on Live is a poor show by Microsoft, considering you have to pay for it. I honestly wouldn't say the 360 has "better online", certainly not in my experience anyway. But if Live was free, I would have no problems with the service whatsoever.
^^^I kinda rambled on for a while there, but you can't say I didn't add to the thread, lol.
