Like many here, I use both services. The core online gaming (lag, latency, disconnects) is the same on Live as it is on PSN. This is to be expected with peer to peer networking. Live is better in terms of online features. The party voice chat on Live is a feature that Sony needs to implement. Also, it shouldn't be a mystery when my friends come online, or if they send me a message. Live does a nice job of notifying me of these things. Unfortunately, Live comes with a cost. I buy all of my multiplatform games on PS3, because I don't know for certain that I will pay for Live every year.
Edit: The friends status and message notification refers to when I start the system. When I start the 360 it does a better job of giving me a friend/message status.
Thanks for the input, Jeff.
