Thanks for all the posts on this. It seems like Uber is going to be the best option, and a decent tip will probably stop the driver complaining it's such a short journey for him.

As others have pointed out, it's a nightmare going between the International Terminal and anywhere else in the airport if you are not airside. I've nearly missed flights in the past because of waiting 45 mins for the international shuttle bus from the car rental place before.

That said, connecting international to domestic is always a breeze and easy in ATL as long as you stay airside.