We spent 3 weeks in Italy. Hired a car in Milan - drove it around and then dropped it off in Rome at the Hassler (near where you're staying). I can tell you that getting into Rome was simply awful. Took us forever (about 45 minutes to go the last 3 blocks!). With no wrong turns (I'm a very good navigator).

By the way - we had very good luck negotiating "day rates" with a local taxi driver we found at a cab stand to take us around the city and outside for sightseeing. Any possibility of doing something like that for your trip from Sorrento? Robyn