So, agree regards Rome. Would highly recommend a Royal excursion on that port day. The port is quite some distance from the city, and inevitably the big attractions (colosseum in particular) have long queues if you do it yourself. You don't want to get left behind.
Barcelona we did ourselves, but was slightly hectic. Tourist bus around the city gives a good overview of the city and we had pre-booked the Cathedral (which is spectacular).
Florence again, I remember being a drive between port and city. I did a Royal excursion which was essentially a brief tour and then 3 or so hours of free time.