My honest normal average mileage over a tank is 30mpg with my 04 jetta wagon TDI 5 speed auto. That sounds horrible for a TDI but my previous car was an 03 pontiac vibe, little smaller and around the same power, and I averaged around 22mpg with that. I do too many short trips to get good mileage unless maybe I had a hybrid. My 46mpg trip was in flat Ohio where most of the time the speed limit was 55-60 so it was about as good of a scenario as it gets. I normally get right around 40mpg on longer trips in hilly Wv.
I bought my TDI because I had never had a diesel and just wanted to play with one, didn't hurt that it came up for sale way cheaper than normal either. My jetta is a good sized car that is loaded with about everything you could get in 04 other than leather, has a really nice ride, decent power, gets good mileage, and it was cheap. It is a much nicer car than anything else that can get close to the same mileage for anywhere near what I paid. If it had a manual trans it would be perfect. Now if I were buying a much more expensive used or new car I would probably buy something else.