I've rented from Avis, Hertz and National at Tampa and have had good luck with all three. Avis and Hertz are in the terminal, with National you have to take a shuttle to their lot. I wouldn't let that deter you if you get the best rate with National, the lot is basically on the way out of the airport, so it probably only adds 10-15 minutes to your time to get off of airport property.