The MPS is great fun for a while, but the gears are a joke when cold and it becomes a pain to drive. Alot of car for the money, but I wouldnt buy another
The M3 is the ovbious choice for performance at this kind on money, but again very expensive to run and there are no shortcuts here.
The S3, is again an outstanding performer here, but you will get bored of the drive very quickly and demand more power, which will just make it fast and still boring.
mk5 GTI/ED30 are both simply too slow in std form. This is probably the route to go down if you are interested in modding.
The 330, again a good choice, but once stuff starts to go wrong prepare for a good hard shafting by the dealers.
Simple winner here is the R32 mk5. It wont go wrong like your mk4 either.