I prefer PSN because I mostly use online services for online gaming (well, and demoes from time to time) and PSN is free. Live is surely not expensive, not at all, but I don't play online very often, so I don't see a reason to pay for something that I don't use very often. And when it comes to pure online gaming Live and PSN are pretty equal: both are completely lag-free (well, depends on the game sometimes) and there are annoying kids on both platforms .
Furthermore, I have my friends on PSN, and since I bought my 360 in April this year I only played for around 10-12 hours on Live, so I don't have any friends there at all :/
2012 - Top 3 [so far]
#1 #2 #3