I have right now a couple of F2's, a F4, an F5 and an F100. I recently sold my F3 that I had forever because it was the one F I never used.
F2 -Just a great classic camera that I can't give up. Everyone should have 2 or 3. You can do it all with this camera.
F3 - a great, tough light camera. Flash is a PIA and I gave up using it whenever I needed flash (that's what drove me to the F4). Never understood the cult following of the FM series when the F3 was a far better camera and about the same size.
F4, a brick after the F3 but really no bigger than the F2, F100 or F5. Great metering system with all lenses, still allows the use of non-AI, great controls and does auto focus. Not battery hungry.
F5, great camera, marginally better than the F100 except trying to depress the lock and turn it on drives me crazy, especially if I'm wearing gloves. Supposedly better / faster AF. Don't really know I just never got the hang of AF and end up with more out of focus shots then I do with manual focus.
F100 best of the bunch if your into AF and a trizillion flash metering modes.
Bottom line I have the 80`200 /2.8 AF lens and couple of other AF lens so I keep and use the F100. However I still have a lot of great manual lenses and even with AF still manually focus most of the time. Both the F100 and F5 are just too complicated for this old guy. Therefore the F4 is my favorite.