A4 vs. A6 used avant

I am leaning toward purchasing a used avant for the wife and would like to know opinions on years and transmissions and engines from people w/ experience. I have a mechanic telling me the 1.8T's are problematic. He also states that the automatics are probably not the best choice for longevity, but I would like to get an auto for her. Probably looking at something in the 50K-80K range. Thanx in advance. andy