I have been at the JFK T4 club a few times when it has been just a mob scene. The funny thing is that it can clear out so quickly that you would think the fire alarm had been pulled. last time I was there i lucked in to one of the business pods/desks facing the windows but all other seats were taken. In about 20 minutes, i looked up and thought the rapture had happened: it was a ghost town. I assume a few international flights left around the same time.
As for ATL B club: its hit or miss for me. I do prefer the slightly better food options that T, A, C and D don't. E and F do but those can be a touch out of the way.
I do hope that the B club brings back the self serve soda machine. Sometimes getting a drink at the bar is like waiting in line to get U2 tickets.