I think the deciding factors is eventually the running cost for the console. PS3 at the moment is cheaper to start with but if you planning to buy lots of games then it will dry up your pocket very quickly.

Xbox360 on the other hand cost a little more because it can play ahem games. Almost all games are multi-platform now(even Final Fantasy 13) and most games looks and play identical(and if there is any differences is so little you won't be able to tell the differences unless you examine it closely which is pointless). So in the long run you can play all the games without burning a hole in your pocket.

I have both system and at the moment i play mostly the 360 because its got more game choices than the PS3. So the decision is yours as to which to buy.