I went through Atlanta last week, from Madrid, very efficient, off the plane, immigration was easy, we were through in less than five to ten minutes, ironically, we were through faster than the Global Entry people, looked like lots of people who never used the kiosks and the line backed up, many went over to the "lower class" immigration line to get through. Checked bags did seem to take a little longer than usual, but dropped the bag at recheck, through security (just put stuff through the x-ray, they use the old style portals, not the body scanners, so no removing shoes), and out into Concourse E. We were early landing, so were into the concourse about our scheduled landing time.
Atlanta may be one of the busiest airports in the world, but you would never know it, very efficiently laid out, since it is mostly Delta, they can schedule flights so that 20 flights do not hit immigration at the same time, would pick Atlanta over JFK, Newark, LAX, ORD, and others any day of the week.