Alamo and National are both located in the same location on Service Road, which is in the airport grounds; the shuttle runs every few minutes between the terminal and the rental counter, so it is not that big a deal, and the ride is less than 5 minutes. The other rental agencies (Hertz, Enterprise, etc) are located within 50 meters or so of the terminal, so you just walk up, check in, grab your car and go. I have used both the walk up, and shuttle at TPA... and given the choice I would just take the walk up (no loading and unloading on the shuttle, tipping the driver, waiting for other passengers, etc)... But the shuttle is not that big a deal. If I could save $20 on a rental using the shuttle, I'd do it.