For me, it has to be Florence. It is astoundingly beautiful, not too big to walk round, and has the most amazing artwork, gardens and buildings of anywhere I’ve been.
Of the places you mentioned, Verona is beautiful, can be done in a day. I found Naples a bit too edgy, I wouldn’t walk round after dark if you know what I mean.
One of the most interesting cities I’ve been to is Dresden, the work to repair the damage left by the war, and the impressiveness of the communist restorations is quite fascinating, it was also very friendly there, not sure that they get a large number of foreign tourists, we certainly didn’t hear lots of British voices.