I've never had a problem at LAX immigration. It's not my favorite airport for departing or arriving (which I did many times when I lived in San Diego), but it's an easy US entry and good for transit.
DFW has to be my least favorite airport.
I'm not a big fan of JFK from my days of doing JetBlue's AllYouCanJet, to go between terminals you have to exit and reenter security. JFK immigration was always jammed and getting luggage and stuff felt like you were in a 3rd world airport.
Delta's Cincinnati hub is really nice and I've never had any issues with Denver, though I've never done immigration at either. Atlanta has always had smooth immigration. Stick with the non-MegaCity hubs and life would be much better I imagine. YMMV of course.