Can't go wrong with an F3. And the prices of both are about the same on e-bay. I have been eyeballing F100's for the last few days and will probably get one. I would not spend over $400.00 for either one. I do have two F3's, one HP and a regular which both are still my goto cameras when in my mind, have to get the shot I want. I am thinking about the F100 for the weight reduction and retiring my F4s. ( well, semi- retirement ) If, well when I get an F100, I will at least be used to the control layout for when I get an F5, unless I find a killer deal on the F5 before. I have AI glass from other older Nikon's and only two lens' that are AF, and compatible for a F100, so there is something else to think about before upgrading.
The F3 is still my favorite film body. I like it better than the F4/5/6 and any lesser body. You just can't go wrong with the F3. I do prefer mine most of the time with it's MD-4 motor drive attached, just gives me more to hold onto.