I'd go with the Nikon F-series since I had learned on those and for me the layout of controls and the sturdiness of the thing is quite solid.
The only thing you have to look out for in these like the F3 is that the little wheat lights might not be working anymore or the small LCD readout (when you look inot the viewfinder) which also on mine quit.
Plus with these bodies you can buy the top (viewfinder..if still available) and replace them or replace the body when one of them quits on you, you don't have to buy the whole camera all over again.
I've had the F1, F2 and F3 and had also had my hands on some FA's and the FM series. All rock solid.
..as for Pentax, digital is my first foray on them and I am actually looking for a good film body..the reason why I suddenly turned up in this thread.
I was looking for the Pentax AF series though that are not cripple mounted.
I'm still researching and I might just open up a different thread just for that so that I can use my lenses for my K100D super on that too!
I was planning on getting an Auto 110 but found out that Kodak quit making the film for it.