Travel advice needed - Vienna v Salzburg

Already posted this on Fodor’s website, but seeking opinions from the Dopers as well. =)
Heading to Europe in mid September for a 2-week vacation. We’re looking at a full week in Paris, a few days in London to see some friends, and are considering a 3-day stay in either Vienna or Salzburg, to take advantage of the Mozart celebrations this year.

So first question, is either city worth seeing for a mere 3 days? That is, should I bother going at all for such a short amount of time? Or would it make more sense to come back at a future date for a full week in those cities?

Second, if it IS worth going for a quick trip, any suggestions on which city to go to?

I found both Vienna and Salzburg to be kind of sleepy and a bit dull, but of the two, Vienna was the more interesting for me. I think you could get a sense of Vienna in 3 days. If you go, you should look into taking the Third Man Tour, it was the highlight of the city for me.

Vienna would feel rushed in 3 days, but I think you could get a good sense of Salzburg in that time. It’s not a really large town and it’s easily negotiable on foot. It’s finite and graspable quickly in a way that Vienna isn’t so much, IMO. And it’s gorgeous in a cute and quaint way, where Vienna is beautiful but is a city.

For three days, probably Salzburg. The castle is there and the place is just lousy with old churches. You can also do the salt mine tour and cross the border to Berchtesgaden, if you’re bored.

I’ve seen both, and I liked Salzburg better. With three days, you’ll have time to do quite a lot of touristy things, and since it’s a fairly small city, a walking tour is tons of fun.