PS3 is just uninteresting to me. Most of the better players use 360 anyways or at least prefer it. And the controller is garbage. You see more people using sticks and converters for 360 controllers than you do PS3 controllers. Analog stick is too sensitive, flys all over the place. D-pad is just too small, and because of that you get input errors a lot. The 360 joystick is my personal favorite.
PC is usually for the competitive games like Starcraft and shooters. And the only reason I think PS3 is even used more is because according to tournament hosts, 360 lags. Which is a bold-faced lie. It works just as well as PS3. So because of that, PS3 is basically the go to console at tournaments. That's the only reason I see that it's used more.
In SC and DoA5 360 has the better players. I don't know about the other major games, but so far from my experience, it's been 360 that people use online and for most casual play. I hardly see PS3's. I only saw a whole lot at them at NCR which was for tourney play sooooo, yeah.