I have never driven one, but as a whole, Audi build some great cars, with very good engines.
The older TT's (the first batch) were supposedly a bit of a nightmare to drive hard on twisty roads, but as an everyday car they're very good.
If you're after a good roadster also have a look at the Honda S2000 (one of the best in it's class), the Mazda Mx-5 (a legend in its own right) and also if you want something German, the BMW Z4 is a great little car!