i have a b6 1.8t...no complaints. these cars aren't terribly difficult for DIY stuff, there's forums out there with lots of info. Stay up on your maintenance and make sure to find a clean used one and you'll be fine.
but parts can be expensive for audis. and modding the jetta is going to cost probably about the same. i'd say get the vw except...jettas just don't have the presence of a clean b6
good luck!