In my opinion, I'd let the 14 year old boy choose...if he's anything like my DS, he wants a specific game system for a specific reason.
My DS (19) has both the PS3 and the Xbox 360. He got the PS3 for Christmas 2 years ago. He bought the Xbox 360 a month or so ago, from his paycheck.
Some key differences: with the PS3, it has built in ethernet so you can go online to play games. With the Xbox, you either have to set it up right by your router to plug it in with an ethernet cable. If it's too far away, you have to by an adapter (about $90-$100).
The Xbox has a monthly fee to play online, the PS3 does not. I'm not sure what that fee is, as DS pays for it himself.
In addition, the Xbox is available in 3 different configurations. I don't think the cheapest one has a hard drive. DS bought the mid-priced one.
Different games are available for each, and often not available on the competing product.
Personally, I'd ask DS specifically which one he wants, and why. Make him do a bit of research, so you end up buying the right system for his needs/wants.