My preference is the PS3. I prefer the controller, the free online system which tbh isn't that far behind Xbox Live. Playstation+ is cheaper than Live, and offers you access to BETAs, free games, avatars, themes etc etc.
As a media center it's incredible, Blu Ray really is just fantastic. It destroyed 'HD DVD' within months for a reason. BBC iPlayer on PS3 now offers HD as well. 4OD and ITV player are also there, with Love Film linking with your subscription so if you're subscribed to them already you should be able to stream movies for free. It also means games that are 2-3 disks on the Xbox are on one lovely Blu Ray disk for the PS3.
List of omfg Playstation Exclusives...
Final Fantasy Versus XIII (To be released but if you're a FF fan then it's a no brainer really)
Uncharted series (really...REALLY amazing games, with the 3rd being released next month)
Resistance series (for a launch game, Fall of Man was ahead of it's time. Online is dead now but campaign is pretty fun, the sequel was a huge let down to most with online being retarded. The 3rd has just been released and while it isn't as good as the original, the online is fun and the campaign is pretty amazing for a FPS campaign)
God of War series (1+2 HD remixes) - Probably the best hack and slash action games ever. They are incredible.
Little Big Planet
Metal Gear Solid 4 (oooomg what a game, if you're a fan of the series and have yet to play, this is enough reason to get a PS3 imo)
There are a few others but I can't remember them all right now.