Xbox Live has had plenty of time to get things right. The party system, achievements, voice chat, gamertags, customization, interface, market, it's all very seamless. PSN had a horrid interface and was overall a pain to use the first few years. It's gotten better but so has XBL. Also let's not forget the whole PSN hack fiasco.
I wasn't a GOW fan but Halo is much more competitive FPS than Killzone which IMO was pretty broken and felt clunky. Uncharted and Last of Us are ok additions but honestly no one bought those games to play the multiplayer.
Personally I miss the classic blades 360 dashboard had. I honestly think its worst. I have harder time now finding what I'm looking for on XBL. I won't call PSN great but I haven't had much trouble with it.
What about the PSN fiasco? Maybe I was lucky but PSN went down yet that weekend I was playing Killzone 2 online because they were doing double XP. I think people were more upset they couldnt get the newest CoD DLC so made a big fuss.
Between my 2 RRoD and the server issues XBL had, like when CoD4 and Halo 3 released and no one could log in for 2 weeks, Ive had more lost time there.
Killzone 3 is very popular and very competitive. Same goes for Uncharted and Last of Us MP. Uncharted 3 multiplayer is strong and Last of Us is well loved, they even just added a few new game type for LoU. They are still adding maps to UC3 so someone must be playign them.
Shame if you havent tried any of them since thats what it sounds like to me. Both KZ3 and UC3 is on PSN for free, up to a certain rank. I admit to be very skeptical at first but Im very glad I gave them a chance.
http://www.polygon.com/2013/9/4/4692936/uncharted-3-labo-u-r-day-celebration-and-lab-map-dlc
http://www.polygon.com/2013/8/28/4670130/the-last-of-us-update-interrogation-mode-multiplayer