I've been traveling to Phoenix several times a month for work and am slowly working my way through all of the rental car centers out of Sky Harbor. Fox isn't the worst (I've reserved that award for Advantage/E-Z), but they also aren't the best. Still, I feel like it's a decent deal if you're able to secure a good price, which for me is anything less than the cost of Ubering to/from the office.
The line was long and moved slowly when I picked up the car, but Dana (the agent who helped me) was friendly and got me out the door super fast. It helps to be a returning customer.
My Yaris was fairly new and clean (compared to the beaters at Advantage), and was a reliable ride for my trip. The fuel gauge took *FOREVER* to register as full after I refilled it, causing me to go to 3 Circle K's trying to essentially top off the car and not get dinged for returning it less than full. Huge pain in the ass, along with having to go on a scavenger hunt to find a staff member when I wanted to return the car.
If anyone deserves fast service, it's people trying to drop off a car to make a flight. Please help your customers out and save me the grief of running through a parking garage with my wheelie carry-on in 117 degree heat! Thanks y'all. :-)
I'd come back because of the rates and relative reliability. Probably your best option in the "budget" rental category.