Fs are great to load, because a damned hinged door doesn't get in your way when you are loading! Just hold the door in your teeth.
I find the Barnack Leicas (and, I assume, other bottom-loading cameras without a back door) are the most difficult to load of all cameras I have used. They can certainly be reloaded in a reasonable amount of time, though. It takes me about a minute. The M series, with their back door, take care of the hardest part of loading the thread mount bodies, i.e. getting both rows of sprocket holes over their respective sprockets, and the film all the way down into the slot so that the image is not exposed onto the sprocket holes on one side, all while working blindly from the top. With the Ms, you just open the back door and position the film.
Loading any 35mm SLR is easy as pie, IMHO. I don't see what is causing the problems with run-of-the-mill Nikons.
The easiest loading cameras I have used are probably anything with the Canon QL system. Boy, do I wish the F-1s had included this feature.