It's difficult to choose between these two cameras. They are different in so many ways.
The F3HP is a joy to use. It's very well made. It's relatively small for its build quality, and it's great if you prefer to use aperture priority. Metered manual is okay but the metering display is not my favourite. Using flash is tricky because there is no traditional hot shoe. Flash sync is quite slow (1/80 if memory serves). You can attach a motor drive and go like stink, or carry the camera without for portability.
The F4S will run autofocus lenses (including AF-S) and is the best AF body to use with manual Nikkors (matrix metering works with AI and newer lenses, although not AI-converted Nikkors). It has built-in spot metering that works with all lenses. It's got a faster motor drive if you like to be able to see what you're shooting (5.7 fps versus 5 fps; the F3 can do 6 fps if you lock the mirror up though). It can be made small with an MB-20 grip but these grips are in short supply and are expensive.
I have one of each and I like both, but they are not at all alike.