I'm a guy who typically chides people for trying to accomplish too much in a short amount of time, but I think 3 nights per city is doable. You won't "complete" big cities like Munich in 3 days (or 3 weeks), but it will let you see the highlights of cities without being too rushed.
That said, if you did want to skip one, I'd recommend cutting Budapest. That would allow you to add an extra night to Vienna for a daytrip to Bratislava, and a couple extra nights in Munich that would allow you to explore more of Bavaria.
Last edited by linglingfool; Jul 7, 2014 at 8:45 am
Reason: Clarification