I've not really travelled too extensively (working on that), but my other favourite European city would be Florence. It's just such a lovely place, if you like art you'll be swamped in it, it's churches rival anything in Europe, and the whole place just has a great vibe to it. The ice cream is exceptional, and it's pretty reasonably priced. The hill the other side of the river from the city gives you a spectacular view, and is a great place to sit and have a few drinks on a warm evening. I genuinely prefer Florence to Venice, where they just seem to hate tourists despite being utterly dependant on them (don't get me wrong, it's a lovely place, but no more than you expect), and whilst Rome is also amazing, I just felt much more comfortable/happy in Florence.
Sticking with Italy, Pisa is maybe worth a few hours of your time, if that. The tower, and everything of interest, is in a two-acre or so site, and the rest of the city is a crumbling, urban mess. They charge you about €30 (I think) for 30mins up the tower and back, and actually when you see it it's not that tall. The other buildings on the site are nice, but they charge you to visit every single one. Stay in Florence (or Siena, which is supposed to be brilliant too) which is an hour's train (for like €7 return) away, and spend a morning in Pisa, it's not worth spending any more time there.
Also, I really don't think Vienna is worth a visit. It used to be fashionable to have a summer palace there, and it was practically untouched by the World Wars, so they're all intact. They've got so many buildings that should be museums, that they end up being McDonalds and Subways, which kind of ruins them. I spent a day there, and that felt like enough to me, after wandering around there wasn't really much to do. The Natural History museum is ok, but it's an old-style museum, which consists mainly of stuffed animals, and 4 rooms of case after case of mineral samples. The main church is nice too, but Prague, Florence, the Vatican, etc all out-shine it.