The thing with the PS3 is that it's better value than the Elite. For £50 more you get a BR player, free online gaming, a media centre (which is not to be sniffed at- I use the 'non gaming' side of the PS3 far more than playing games- always have as well) and little things which are better than the Xbox (iPlayer and wireless net access are a couple of things).
Even if you want to only play games, it'd be worth sticking an extra £50 and getting a PS3 in my opinion.
Of course, if there're certain games you want to play then go for the console which has those games as exclusives. I doubt that's the case though otherwise you wouldn't have wasted time asking on here?