In the last year or so I've sampled several US airports. The worst by far was LAX, with queues so long and slow that I only just caught a connecting flight, which was due to depart 2 hours 20 minutes after we arrived. Someone making the same trip a few days later got a 23 hour holiday in LA, courtesy of AA. Part of the problem was the arrival of several flights close together, but a possibly greater factor was that this rush appeared to coincide with a shift change for the immigration officers.
I don't recall JFK, SFO or IAD being anything like as bad, but by far my quickest experience was a SAN. it may have helped that I was travelling with someone who was using a wheelchair and we got taken to the shortest US Citizens line, even with UK passports, but other people semed to get through almost as fast.