We have hired a limo a few times and also enjoyed the easiness of it. Just depends on which port we're in. Last time we were surprised to have a stretch Lincoln Navigator deliver us home. What a treat!
I grew up on Merritt Island/Cocoa Beach/Port Canaveral so I rent a car to visit former classmates around the area. When I suggested a rental car, I would not rent it for the week only to pay to park in while on a cruise. That would be a waste of money. Rent it, drive it for a day or two, turn it in with reservations to rent it again upon your return to port. It is just a matter of personal preference and like you said, you have to factor in the number of passengers and luggage.
Also, if you get a great deal for a weekly rental, there are a few hotels than offer cruise&park packages.
pnaples, I have read on these boards many people recommending Legacy Limo service but have never tried them.
Have a great cruise everyone.
Teresa and Larry
#36-Carnival Splendor 9/16/12
7 night Mexican Riviera
#37-Allure of the Seas 11/11/12
7 night Eastern Caribbean
#38-Celebrity Solstice 4/8/13
17 night Tahiti -- Sydney-Honolulu
40th Anniversary Celebration
270 days at see; soon to be 302