ATL - Hertz is very good but National has excellent service out here. They might not have the best selection of cars on the regular/Exec. Aisles (check out my thread in this forum) but when it comes to efficiency, very good customer service and getting out of the rental lot, nothing beats National with 6 or so exit booths.

PHX - National is just a tad better than Hertz simply because of the vast selection of cars out there. The only downside is the not so friendly staff (perhaps because I'm not a frequent renter out there).