Madrid to Barcelona do I stop in Zaragoza

We stopped in Zaragoza it was just alright; pictures of it looked better than actually seeing it in person. Since you've been to Madrid before, try it. Something about its location has an effect on the kind of weather it gets there in a bad way in the winter for sure compared to Madrid and Barcelona. If you have not been to Barcelona before make sure to pay extra attention to your valuables, especially in crowds.

Spent 2 nights in Zaragoza in 2022 as part of a much longer trip. I feel that was a good amount of time. We did have a car.

Seven nights isn’t long, so if you plan on visiting Zaragoza, I’d keep the Madrid portion to a minimum since there are plenty of sites to visit in Barcelona. With a festival occurring while you are there, there should be a lot of options in Barcelona.

I think I will just go to Barcelona. Is it better to fly or train.

The Aljaferia Palace is awesome and well worth making a stop in Zaragoza.

... better to fly or train.

The train takes 3 hours and the security check is not as extensive as at an airport. You just need to arrive 30 minutes before departure to catch the train compared to the recommended two hours for catching a domestic flight.

The train leaves from the city and arrives in the city; a flight requires you to commute further to and from where each airport is located. Each airport is around 8 to 10 miles out of the city in the suburbs sort of how O'Hare is in Chicago.

The train experience is less stressful.

If you had more time, I would give a definite yes to Zaragoza. However, I would consider 2 destinations in 7 nights a maximum. Save Zaragoza for another trip.