I actually find "classic" Nikons quite easy to load.
(Even the notorious F, just like later Leica Ms).

35mm Rolleiflex and Leica SLRs need the "reverse loading" a previous post described (insert film end in take-up reel first...). Only the Rolleiflex 3003 (and its brothers) can be something of a pain to load... Luckily several magazines can be pre-loaded beforehand and the counter doesn't advance unless the film does. :-)

I also find the Pentax 6x7 pretty akward: I'll certainly try the trick of not removing the tape until the spool is in place.