Ummm, that's kind of like asking - if I go to the States, where should I go. lol. What kind of budget are you on? How long are you staying in the EU? Those will all dictate where you go. Contrary to what many think, Europe still takes a while to get from one side to the other, without taking a plane.
Having that said:
Prague I've heard many good things about.
Barcelona (probably the best nightlife in Europe, perhaps next to Ibiza).
Napoli and the Amalfi Coast
Brighton (South UK)
... again, it really depends what you are looking for, how much time you have, and what kind of budget you are on.
Btw, I think the autostrada is better than the autobahn.