Nikon's first SLR, the F, the first revolution.
The Nikon F2 was just a reworked F.
The Nikon F3 was an electronic F2, still merely evolution, not revolution.
The F4 is the world's first professional autofocus camera. Today, slow but not bad.
The F4 is the world's first professional camera with a built-in motor drive.
The F4 is the world's first professional camera with modern Matrix (intelligent) light metering.
The F5 was simply the F4 in a tougher package, but with knobs replaced by buttons and menus. The F4 has dedicated knobs for everything. The F5's meter is worse than the F4's when used with manual focus lenses.
The F6 is a lighter-duty F5, but at least one can get Matrix metering with manual focus lenses on the F6, which the F5 can't. You have to program menus to get matrix metering with manual lenses on the F6; all you have to do on the F4 is mount a lens.
In my opinion, you can choise F4 (without F4s, F4e because its heavy) is the best for AI/AIS.