TBH, IME, DEN is one of the worst locations in the rental industry--across all companies.

We have seen more complaints about DEN than probably any other single airport. Complaints range from running out of cars to extreme waits at counter to poor vehicle condition/cleanliness to sneaky counter agents adding charges to bills and more. And the complaints are with everyone--Hertz, Dollar, Budget, Avis, Alamo, etc. etc.

Not sure what attracts such poor-quality operations managers to the Mile High City but just be prepared, no matter who you choose to rent from. Come with a printout of your reservation straight from the rental company's website (so they can't argue when you challenge them for why the price is higher), book with a rental company loyalty program (so you can skip the line and be first in line if they've run out of cars), take a walk-around video of your car before you leave and point out any damage, and don't forget to fill up with gas before getting close to the airport as the one gas station out at the airport charges a rip-off premium price. (Sapp Bros. off of Quebec usually has the best prices, but check GasBuddy.)