One more place ... Where? :)

Any of the places you list would be worth visiting, but the one that I think makes the most sense in combination with the rest of your itinerary and taking into account your love of scenery, ambiance, and frugality, is Florence. The city itself is a gorgeous museum filled with gorgeous museums. And if you are willing to take a day to explore the surrounding countryside, you'll see some beautiful scenery and charming villages. Plus the hassle of getting there from Sorrento or of getting from there to Paris is relatively small.

Barcelona and Berlin are places where you'd benefit by having far more than 3 nights. (Well, that might be OK for Berlin if you're uninterested in WW II and Cold War history, but in that case, Berlin probably wouldn't be on your short list.) I wouldn't want the hassle of flying into and out of either of those cities--which are favorites of mine--for what would turn out to be just about 2 days of sightseeing time. I have no recent experience with either Budapest of Florence.

With only 3 nights to play with, I'd try to come up with an interesting place that is a short train/bus ride from either Sorrento or Paris so I'd only have one intra-European flight to deal with. My first thought was Alsace, but perhaps Florence would work well. Not sure about hotel costs in those areas. Both are likely considerably higher than Berlin.

I've done something similar and would recommend taking the high speed train from Naples to Florence or Rome. Or stay put in the Almalfi/Naples region. From Sorrento, you can book a bus ride out to Amalfi and, if you are music lover, maybe even get concert tickets in Ravello. You might take a tour down to Herculeum and Pompeii and spend time in the museum in Naples. You could spend a couple nights in Positano and take a little hike to the Gods along the Amalfi coast. This area is worth a deep visit. The rest of Italy awaits your next trip. Just saying. Betsy Bell

I realize you have already done the Amalfi coast, so Florence or Rome would be my vote. I just spend several days near Lucca and loved, loved that medieval walled village, accessible by train from Naples. Betsy Bell

Also put me in for Florence.
When you get to Sorrento, don't be surprised if the weather's a little cool with average lows of 41 degrees F and average highs of 57 degrees. December's also the wettest month of the year.
I'm just saying dress for just about anything on winter trips to Europe.

It's so kind to all of you to take the time to help us. Thank you!
Yep, I think it makes more sense to spend those three nights in Italy ( not something to complain about! )
* Love the idea of attending a concert in Ravello!
* We traveled to AC in February last time and we loved it, I imagine the weather in April can only be better.
* With only three days last time, we didn't get the opportunity to experience some of the places you mentioned, we hope this time we can do it and have an even better holiday!
* I'll check info posted on this site about getting from Sorrento/ Napoli to Florence and best places to go from there by bus / train.
I'll look for more help with things I don't find.

Thank you very much!

Take into account that April 16 is Easter Sunday. That is a very busy weekend. Easter is the biggest holiday in most of Europe and closures are similar to Christmas in North America.

Chani has a good point. And know that in many countries in Europe, the day after Easter is also considered a holiday, with many places closed and others very crowded.

Oh that's right! Thanks for the reminder. Traveling that day wouldn't be a good idea, right? It would be better to already be in Paris by that day, I suppose ... Thank you!