Currently playing FFXIII on PS3. I'm almost finished with it. Initially I was going for a platinum trophy, but then i got bored of farming traps/platinum ingots.
Will finish it, and get Yakuza 4 ASAP.
Xbox is probably better for online gamers, as it offers a more reliable service and more fun online exclusives, such as Halo and Gears of War.
However, I prefer PS3 because of the quality of its exclusives. Metal Gear Solid, Heavy Rain, God of War series, Uncharted series, Final Fantasy Versus XIII, Valkyria Chronicles, Yakuza series etc.