Re: Bologna or Florence?
I have never been to Bologna, so I can't give you advice either way on that city. However, I did spend some time in Florence, and it's a wonderful city in itself and a great base for exploring the surrounding towns of Tuscany (like Lucca, Siena, San Gimignano, Cortona, Pisa -- though that last one is a bit overrated in my humble opinion). You can get to most, if not all, of those places by train if you'd rather not rent a car.
Florence has a bunch of great museums, but I actually liked the churches even better; they're a great place to check out the Renaissance artwork the city is known for without having to spend as much time as you would in a museum -- might be a good option for you guys if you don't want to do the museum thing. It's a very walkable city as well.
I actually wrote a trip report about my time in the Florence area, which you can read here if you're interested: Spring Break in Italy. I'd be happy to answer any questions you might have.
Hope this helps a bit! Please let us know what you decide to do.
"I haven't been everywhere yet, but it's on my list." -- Susan Sontag