We always fly into Tampa, and we almost always rent from Dollar. They are at the airport, and we usually have the car within 5-10 minutes.
To get to the car rental counters, you will need to go out the doors at the baggage claim, across the passenger pickup lanes (watch out for cars!) and into another building (it's a total of about 25 yards from the baggage claim). The cars are right behind the car rental counters.
FYI, I don't know if you're interested in a minivan, but I'm getting a minivan for a week from Dollar in late Jan.- early Feb. for $199 ($243 with taxes). We got it from their website under 'Specials'.