I had an N80 which is a US version of F80. I liked that body. It's small, light, and has all the features one would normally expect. It also works with all the modern lenses. I believe N90 can use lens with VR but VR does not function. One small benefit of N80 is that screw type shutter release works.
I never used N90. I have F100 now so I sold my N80 (which I regret somewhat...)
Most of my lenses are AF-S type. Auto-focus speed does not seem to vary much if anything between N80 and F100. I haven't tried screw drive type for comparison purpose.