Media Centre - Probably PS3 - for now, as there isn't a lot you cannot do to a xbox, except the obvious blu ray.
Gaming - Xbox all day long. I mean there is nowt on the PS3 that grabs my attention. AT ALL. GT5 was a massive let down and there are no exclusives on there that make me want to get one at all.
Oh and Forza 4 has just been announced which going by just the initial shots, is going to blow it out of the water.