Although you can't beat the sound from a V6 many of the mk4 boys are throwing 1.8T lumps in theirs. The v6 (although powerful) is heavy. The standard 150 1.8T lump is easily tuneable and can do over 200 bhp after a map and, filter and exhaust work. If you can get the audi 225 1.8T lump from the TT, it's internals are alot stronger so can handle having the excess power alot better.
BTW don't even bother with the 2.0 8V, it only produces 115 bhp. You'd be better off with a lower sized engine than that.