I will obviously say Xbox because I personally own a Xbox Slim 4GB (I only play 4 or 5 games so I don't really need 250GB). Microsoft developed the new Xbox to meet the needs of the gamers, like me and all of you guys. One of the biggest problems the original Xbox had was the dreaded Red Rings of Death (RROD), I don't don't the specifics, but I think they changed the motherboard, like I said, I'm not really sure. The other thing is that the console has slits on the top and side, so it is constantly blowing air out so there is no overheating. The console's power button and the disc button are really "sensitive", so you don't have to push the button hard in order to power up the console. The new Xbox also has a built-in wireless adapter, so you don't need to pay ~$100 for an external wireless adapter.
I haven't seen the new PS3, but it will have its pros and cons. I only mentioned the pros in the new Xbox, but I'm sure that new problems will arise, but for now, I will go with the Xbox Slim.