A bit of a drive from most parts of the Phoenix area but worth it if you want good prices and great service. I rented a ski rack for an overnight trip to Flagstaff. Even though I picked the rack up the day before my trip and dropped it off the day after I returned, I was only charged for one day's rental fee.
Note: be sure to check operating hours with the associates when you pick up your rental. I was told they were open til 7pm on Saturday (even called on the way back into town). Got there at 15mins til and they were already closed. I let management know about this the following day when I returned the rack, but it was a hassle to drive out to Mesa an extra time.