i would say go for a PS3 for several reasons, i don't personally own an xbox 360 but i have played numerous and they are seriously annoyingly noisy, theres just a constant whirling noise which is unforgivable TBH. another factor for me, matt (my best mate) his xbox disk tray gets constantly jammed, and its his third xbox, so reliability isn't great either. you have to pay to play online and even when you get online (halo 3 for example) finding games is a bit tiresome and needlessly time consuming and xbox live is full of annoying american kids whinging about whatever. so IMO PS3 advantages are:
1) they are far less noisy than the xbox 360, the only gripe with the PS3 is the annoying noise the hard disk makes while reading/writing.
2) notably more reliable than the xbox, no stupid disk tray to jam, no red rings of doom.
3) HDD swapping is simple as hell and you can use standard 2.5" SATA drives, which are cheaper and more capacious than the ones you get for the xbox, even the elite.
4) it has a blu-ray player, which to me is no biggy TBH, but apparently a selling point.
5) from a technical perspective, the xbox 360 has a power pack like a breeze block, whereas the PS3 is totally internal, which is impressive i suppose.
6) most games are available on both platforms, little/no difference in price for games and there are quite a few decent PS3 games due out in the not to distant future.