Voted mk1, I'm old enough to remember how far ahead they were of the competition back then, plus they had the purest styling.
My head would have voted mk2 as they were the best engineered car by a long way. I seriously don't think there was a better built car in the price bracket for another 20 years!!! If they didn't get accident damaged or abused they just didn't rust. The interior was spartan but solid as hell and the big bumper cars just looked the cojones.
Aside from the mk6 which I'm thinking over, I've owned at least one example of each exluding the mk3 (where I had two VR6s but not GTIs as they just didn't cut the mustard) so can at least have a valid owners opinion. IMO