I think you have to forego the surprise and ask him, it would be gutting to spend hundreds of quid and discover that he's set his heart on a game that's only on another console. Wii is "best" for family games, but if you get one of the other systems then there will still be lots of suitable games available (eg all the Lego games are available for Playstation AFAIK, and there are lots of Rock Band type games for all the systems).
"driving/ rallying games, maybe some fighting ones (mild world war types, not really violent ones)"
What?, what do you call a fighting game? A beat em up (2d or 3d) where people face each other one on one and participate in fisty cuffs ala Street Fighter?. or a scrolling beat em up where you walk around looking for camp looking guys and S&M ladies to beat up ala Splatterhouse?.
or do you not mean a fighting game? do you mean a shooting game?, what kind?, a shoot em up where you pilot a ship and shoot others ala R-type?, a flight sim where you partake of dog fights in real war situations ala Ace Combat?.
Do you mean a first or third person shooter ala Call of Duty or Gears of War?.
Or do you mean a real time strategy game where you command an entire army in battle ala Total War?.