Budapest, Vienna and ?

My first trip to Europe was with my adult sons! We did Vienna, Budapest, Prague and Munich. It was a lot of fun and very meaningful. I would suggest Prague to you for a few reasons. Prague is very beautiful, relatively close to the other two and shares a lot of history with Vienna and Budapest since they are were a part of the Austro Hungarian empire. Prague can be quite busy, but it'd be quieter in November. We were there in January and we had a lovely time. They sell mulled wine on the streets. If you have the time, you could consider a day trip from Vienna to Bratislava.

I like Spain very much. Madrid is quite lively and pretty. However, I think other cities in Spain are more interesting and have more history. Also, Madrid is quite far from Budapest/Vienna.

I would suggest flying open jaw. Into one city and out of another. We did into Vienna and out of Frankfurt (took a train there from Munich our last stop)

I wish you happy times and great memories!

Ljubljana (Slovenia) and Venice are both in the general area, and both wonderful.

With 10 days keep it close - time, not necessarily distance. Ljubljana is a long haul for instance.

Two ways of looking at it, ground and air. For ground look at Gyor, Eger Pecs. For air you can reach a lot out of Budapest in 1.5 hours flight time (usually under 4.5 hours door to door) and under $100 for the ticket. Go to Google Flights, enter One Way, nonstop and Europe as the destination. You will see the options. Then look for open Jaw tickets into the options you like and out of Vienna back home. I do this all the time and have seen amazing places as a result.

But to be honest, with 10 days, unless you have a burning desire to see some place, I would stick to the ground option.

The classic is Budapest-Vienna-Prague because of the rail connections. For me that would be okay for 12 nights but not for 10. Keep in mind that you need to count nights and the number of days you have is one less. Arrival day usually means getting to your hotel in the early afternoon and struggling to stay awake (jetlag, red-eye flight) until bedtime. Your last day is usually spent just packing and getting to the airport (3 hours pre-flight).

There are day trips from Budapest. From Vienna you could possibly day trip to Brno (1.5 hour train ride) and definitely day trip or spend 1-2 nights in Bratislava (1 hour by train, a little longer by bus), which also has good connections to the Vienna airport.

I'd add Munich or Salzburg--all along the way, start in Budapest, train to Vienna, train to Salzburg and/or Munich then home from there. Or reverse. I've been to all 4 and there's plenty to do in each, 3-4 days would do the bigger cities justice.

Why not day or two in Bratislava? My wife and I just spent a day there this week on our way from Vienna to Budapest. Train is convenient (only an hour from Vienna, about 2.5 to Budapest), the old town is pretty neat, Devin Castle is a great experience given its location where the Iron Curtain was, and both the view and the and the food at the UFO Tower were the best we've had on this trip.

I was looking for something and I came across this. Very useful:

https://www.google.com/amp/s/thepointsguy.com/2017/06/10-things-about-budapest/amp/