It really depends on what kind of games he likes to play
The Wii is more of a family console, based on fun and using the WiiMotes. Graphically, it's not as good as the others, and you can't play DVDs using it.
I don't have an XBox 360, as none of the games on it that aren't also available on the PS3 appeal to me
The PS3 might be more expensive, but it's also better quality, imo. It's also a Blu-Ray player, which is nice. The graphics (if you have an HD TV and connect it with an HDMI cable) are gorgeous. Far outstrip the same game on XBox. We got the Avatar game (of the James Cameron film), and it was stunning. Played the same game on XBox, and yes, it played fine, but it wasn't as pretty
So really depends on how important good graphics are to your OH?
I'd also wait till a bit nearer the time, as a lot of shops will have bundle deals going on as Christmas approaches.