Ironically, I found the most consistent results with my Nikon AFD lenses, came with the older F90x body which I still have, but even that was not totally foolproof, in low light with open aperture I would use manual focus. However, it was when the news publication I used to work for changed over to digital, some years back that the real problems started. For some reason autofocus on Nikon's digital cameras (and I'm talking about the early D1x, D2x etc.) was always slower to lock on than on the F90x, and in some instances it just "hunted" all over the place. The worst thing was the unpredictability of it all. (and this wasn't the only bugbear with digital by a long way).... Yes you could say the later D3 is better in this respect, but in a climate of drastically falling fees etc., it just doesn't make sense to pour yet more thousands moneywise down the "digital dark hole", just to get something that should have worked properly in the first place.
However, since I quit the news business, the pressure to shoot digital is no longer there and i've returned to film cameras, to manual FM2n's. I find them more reliable as cameras and the manual lenses more solidly engineered. For someone brought up with manual cameras, I have no need of all the automated bits and pieces, particularly when they don't always work as they're supposed to, and the AF lenses are often too flimsy to last the course.