I'm trying to decide on a summer vacation destination

I really liked Malaga. It has an incredible mix of different cultural influences and you can take a day trip to Morocco from there. I also like Barcelona with access to all the Gaudi artwork.

My family is from Frankfurt and I spent a little bit of time there while living in Wurzburg a few years ago. To me it's the most industrial looking of the German cities I've been to, but there's lots of museums and sightseeing to do. I personally really loved the filmmaking museum there. However, it wouldn't be my go-to destination for such things in Germany. For museums, parks, and sight-seeing I'd choose Berlin or Munich.

Madrid is not the most attractive of cities; if you're interested in the Iberian peninsula, I'd recommend Lisbon over Madrid. And Granada is wonderful.

Amsterdam?

-cb

How about:

Bratislava. You can afford a luxurious 5 star hotel in the city center there, and then you can get to see a city/country that isn't part of the standard American-does-Euro-tour-lite pattern; also, Vienna is less than an hour by train, so you can see a major European capital as well as a smaller, less visited city from the former Eastern Bloc. European budget airlines go to/from Bratislava and other major European capitals as well.

If it helps, I used to have family in Milan and visited regularly - always had a great time there but if it wasn't for the family interest I can't think of much to recommend it; once you've spent a couple of hours at Duomo you're pretty much done (conversely I have worked in London for about ten years of my career and so never had much of a time there but would recommend it in a heart-beat! Superb city. Truly.)

If you can get to Milan for a good price can you get to Rome? King of cities for interesting things to do!

If food is important to you, I'd choose Madrid.

Madrid is wonderful! Not much to see in Frankfurt by the way. Take it from someone who lived in Germany for quite some time. Moreover, Madrid has really great weather!