We have never used Dollar but have used
Alamo and Thrifty extensively. Alamo is onsite, which is convenient, but they tend to have long lines and many of the agents will hard-sell the insurance and try to trick you into taking it. That's not a problem for me because I am very assertive. And sometimes the line is non-existent...it's hard to predict.
Thrifty is offsite but typically less crowded. If you go with them, sign up for Blue Chip so you can bypass the main counter and use the Blue Chip line. We just rented from them, and with Blue Chip there was no insurance pressure (at the regular counter, they're usually not bad but I did get an agent who copped an attitude when I didn't take it once). Their shuttle service is really prompt and they're not far outside the North Exit of the airport. They also upgraded us a couple of car classes on the last rental.
Barb