I almost always refill the gas tank to avoid the fee, exceptions being when I'm really pressed for time. Even if I haven't driven far, AVIS (my usual choice) seems to check the miles and "refill" themselves. Then the charge for the gas appears later on my credit card.

I do recall that I rarely refilled in ATL because there was no safe place to stop near the airport. That may no longer be the case, as it's been a while since I rented a car at ATL.