I've used both and vote for the F4s...
I started with an F, graduated to the F2s, then got an F3HP with motor drive. Basically got out of it to go autofocus, but also because the motor drive contacts were not reliable on my model, causing it to not shoot sometimes when I needed it to.
I now have the F4s, and use it both in AF and MF modes (not convinced the AF is always spot-on with this camera), and just love the feel and function of it (forgiving the AF fudginess). I also love the feel of the grip for both horizontal and vertical shooting. And I echo others' posts about the built-in diopter correction. I have a hard time with some models that don't have it (like my Nikkormat EL).