“I just love my F3hp and was wondering which full manual Nikon to look into next.”
It depends on why you want another body.
If you just need another body to use, I would simply get another F3.
If you want to add it to a collection of “full manual” Nikons, here is what I would choose in order of priority:
1. Nikon SP rangefinder
2. Nikon F2 titanium
3. Nikon F2
4. Any other Nikon rangefinder
5. Nikon FM3a
6. Any other Nikon FM except FM-10
7. Nikon F
8. Nikon FM-10