Mate it really depends on your gaming preferences and if you are looking at the whole home entertainment package.
I will give you (personal opinion only) pros and cons so you are not making a choice blind, but at the end of the day get the console that suits your needs best.
XBOX Pros:- Cheaper of the two
- Better controller for FPS (IMHO)
- More stable online play than PSN (IMHO) and communication (voice and message) is more user friendly than the PS3
- A more active online community in most cases.
- Updates are ultra quick
- Exclusives such as HALO series, MASS EFFECT series, Gears of War series, Forza series, etc.
- collects less dust than the PS3 (Laugh if you will, but it does for some reason??)
XBOX Cons:- Not as solid a build as the PS3 (Although later models are better than the old ones)
- Online products are purchased in MS points and most items are way over priced! I hate &$%(*& Microsoft points!
- You have to pay a yearly subscription to play online (offset by a far better online service though)
- Transferring files between consoles is at best a pain in the arse, at worst impossible.
- You have to pay about $150 extra for wireless connectivity (although there is a work around if you PC is close) and you can only use a proprietary hard drive, biggest 120Gb (unless you buy the 250Gb MW2 limited edition console)
PS3 Pros:- Bluray! (If you have a HD tv you need Bluray
)
- Better console for platform games and fighting games
- Better controller for fighting games by a long way and internal battery is better than XBOX battery. (D-Pad is way superior than XBOX D-Pad.)
- Exclusives such as Gran Tourismo, Uncharted series, Killzone, Little Big Planet, etc.
- Online Market place is better (IMHO) than XBOX market place and shows costs in "real" dollars. Also you can use your purchases on up to 5 PS3 consoles.
- You can upgrade the Hard Drive easily and are not limited to proprietary units. (I upgraded both of mine with 500gb HDD for less than the price of 1 X 120Gb XBOX HDD).
- Now has the ability to record HD and SD TV (With Play TV)
- Ability to pair your PS3 with a PSP or PSP-GO for some cool features
- Many USB PC devices will work on the PS3, such as Keyboards, headsets, etc.
- Bluetooh connectivity
- Logitech make the best racer steering wheel and it is exclusive to the PS3 (oh and PC, but we are not talking about PC's!
)
PS3 cons:- Online connectivity is not as stable as XBOX Live (but it is free
) Online gaming is far easier and more stable on the XBOX
- Updates take FOREVER on the PS3 compared to XBOX. This is my biggest pet hate of the PS3 ... THE $#%&^&%^ UPDATES! They are constant and take forever to download!
- Online comunication is a pain in the arse. I still can't get the hang of the mail system and have missed many messages
XBOX has this hands down over the PS3
- The dust I mentioned earlier (but I don't know if this applies to the new slim models??)
- Gamer points are cooler than Trophies IMHO
)
- No Master Chief!

As I said go with what suits your needs best. As a media unit, the PS3 is far superior with the Bluray, but both can play MPEG 4, DIVX, WMA, etc.
IMHO the XBOX "feels" better for gaming (especially FPS's) but the PS3 is closing the gap at a rapid pace (and fighting games blow chunks on the XBOX unless you fork out for an arcade stick). In the graphics department they are about the same.
So if it is only for gaming I would recommend the XBOX 360.
For a complete entertainment unit (especially if you want a good Bluray player) I recommend the PS3.
My ultimate recommendation though ... Get them both!
See Click's PS3 guide
here
See my XBOX 360 guide
here