Padova or Bologna for four nights

My vote would be Bologna. While it may not have sites to compare with the Scrovegni Chapel, it is a fabulous city for just wandering around. Food options abound. Plus it's a great transportation hub. You could visit Ravenna, Modena, Parma or Padova as a day trip.

There will be plenty to do, whichever you choose, because both cities have many good day-trips. To me it would depend to a considerable degree on which side-trips most attracted me. You will need to make another trip to Italy to see all the worthwhile destinations you miss this time.

Ferrara is a quick trip from either base. I haven't been there, but it gets great reviews from those who have. What's not to like about an historic, atmospheric city with few foreign tourists?

Padua is a more convenient base for visiting Vicenza, Treviso, Bassano del Grappa and Udine (but Udine is over 2 hours each way). You could also take a long day-trip to Lake Garda, but that's not something I'd recommend.

Bologna is a more convenient base for visiting Ravenna, Modena and Parma.

Personally, I'd go with Bologna if you haven't been to Ravenna yet.

Bologna for sure. We only spent a week there but have considered returning for a month. The architecture, food scene and energy from Europe’s oldest university contribute to a wonderful, walkable city. We left our car in a garage adjacent to our hotel during our stay in Bologna. We had come from the Dolomites and we’re going to Tuscany next.

I have a pencilled in plan for more days than 4 for that area and I wanted to use Fererra as 'home base'. It isn't as completely central and convenient as either of the other 2, but then, I am often contrary on planning, and it would be easier to rent a car from there for a coastal national park visit that Bologna with its parking limitations.
Under the circumstances, I think Bologna has more to offer.

I have stayed in both Bologna and Ferrara. Caught the world guitar expo in Bologna. Caught the flag palio?? (not sure what it was called) in Ferrara. Loved them both. The food in both places is awesome, as is the architecture. Padua we did as a day trip passing through and were not as impressed.

We spent 3 days in Padua in late September and loved every second. We were able to walk everywhere and found the people there to be especially tolerant of our attempts to speak their language and they even spent time coaching us. We found the food wonderful and I indulged myself in great tomatoes that time of year. I actually preferred the food there to that found in Venice. I'm an art historian by training and artist outside of my professional IT life so we spent 2 evenings at the Scrovegni Chapel - "Giotto Under the Stars" gave us double visits and St. Anthony's Basilica has some wonderful pieces. The 800-year old market in the center of town was a daily activity. We would definitely return and in fact commented on how much we would enjoy living there.

I agree with Acraven - if you have no reason to favor one over the other for itself, pick the one whose daytrip possibilities you prefer.

And yes, do try to get to Ferrara from either one. In addition to being very pretty and having few tourists, it's the only Italian city I've seen where bicycles seem to outnumber cars in the center - you'll think you're in Amsterdam or Copenhagen.

Thanks all. Really enjoy reading everyone’s input.

We have decided on Bologna. Thought the comment about picking one with the most side trips made sense. We have been talking about visiting Bologna for our last few trips, hopefully this time we’re going to make it. Will definitely add Padova to our next trip - Good Lord willing.

4 days in either is probably too many; I would pick Bologna but throw in a couple days trips to Padova and Vicenza, both short train rides and each worth a day.

I hope you'll love Bologna as much as I do. When it's hot the many porticoes give welcome relief from the sun. The tour of the University was excellent (and better than that of Padova :-).

Thanks to all who commented. Our Greek Island Cruise departure on May 16th, 2021 has been changed to Ravenna. We arrive in Rome on May 6th so the info in this thread has been very helpful in planning a new itinerary centered around Bologna and Ravenna, two Italian cities we have never visited. If people have B&B recommendations I would love to have them. We like to stay near or in the historic center. If the B&B itself is historic it is even better.