For what it's worth, I DID have a headache with Alamo's location. We went in June, perhaps busier than other times. The shuttle was jam-packed and I had to leave the rest of the family at the airport with the luggage as a result. The center was insanely busy with a line out the door. The Kiosks don't properly read the DL from my state (An Alamo rep elsewhere once told me to skip the lines and go to the Service Desk since that is a known problem with my state, but I did not, felt wrong given how crowded it was) and the regular line took 30 minutes. Waited a bit more for my car. Then, traffic back to the airport was slow-going too.
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On the return, it was easier. The bus arrived in 10 minutes. Traffic still slow at the terminals. United, ours, is the last.
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I use Alamo everywhere else, but I made a note to myself to try one of the onsite companies next time. My experience may have been an outlier.
My 2 cents. Good luck.