He already owns one (check his user profile)
I would advise you to buy a Wii, because it's more different to your PS3 than the 360 is, and the games library is different too.
The Wii has a much better library for local multiplayer - when you have friends over.
The Wii is cheaper, unless you buy the arcade
On the other hand
The 360 has better online multiplayer
the 360 is cheaper if the arcade suits you
So in the end it's personal preference







