Like everyone else has said, Vincent pretty much nailed it. I have played the Wii, and it IS a more "family-oriented" gaming system. I used to have an Xbox 360, up until a couple of months ago. A couple of things that I can add are this...the main two reasons why I got rid of the 360 was #1 having to pay to play. The damn games are already $60, then I have to pay ANOTHER $50 a year just to play my friends?! Nope PS3 is FREE, and free is for me! #2 is the fact that Xbox's customer service SUCKS ASS! Its like pulling teeth just to get sosmething on your account changed, like a credit card, etc. I cancelled my Xbox Live membership when I sold my 360, and was just charged TODAY for another membership!! Needless to say, I called them and got that taken care of. They cancelled a card, but not the card connected to thee account. (I had is set up to where the membership came out of my account every year.) But, like Vincent said, the controllers are DEFINATELY more comfortable on the 360. The ones for the PS3 are decent. I mean hell, if he's had a PS2, then it wont be any different. The 360 controller is just more ergonomic.
That and I sold the 360 so I could get the PS3 for the Blu Ray player. It has most of the same games I like, and I now have a bad ass Blu Ray player.
This is the way I see it, if he's coming into his teen years, he'll want either a PS3, or an Xbox 360. If he prefers to play Halo and Forza 3 Motorsport, then the 360 is the way to go. If YOU dont want to have to pay the extra fees to him to play every year, and if he likes the PS3 specific games, and wants a Blu Ray player, then the PS3 is the way to go. Its like the difference between DirecTv and Dish Network. They are pretty much the exact same thing, other than the fact that DirecTv has sports packages. So, if you like sports, fgo with DirecTv, if not, Dish Network.
I dont think you could go wrong with either or, honestly.