I'm an Olympus fan/user for many years, but with that said, from your list, I'd get one of the Nikons.

Why.

*They made a bunch of them and they are in good supply at reasonable prices.
*Ditto for the Nikkor manual focus lenses, available, inexpensive, good quality.
*Can still be serviced.

If starting out I'd go for the F2 because of the interchangeable finders, and more importantly, interchangeable focusing screens.