MSPeconomist - I hadn't given thought to a difference in rental car costs, although I checked and it's only a $40 difference.
Essentially, the cost differential isn't a driver here for me nor is the drive (at least in concept). I have a 7 hour drive earlier in the week because any connection from conference 1 to conference 2 required a change and at least a one hour drive on either end (hence multiple rentals), so I'm already in for some miles.
What I'm getting is that the ATL connection is less of a concern so it's all about preference. Thanks again for indulging me - I tend to be a contingencies planner. Happy Saturday.