While I am certain that some lenses focus more reliably or faster than others, I feel that the whole DSLR autofocus system that is currently in use is loaded with potential problems and really needs to be replaced with something that will inherently compensate for the imperfect tolerances of both lenses and cameras.
My main camera is a 5D classic, which had a severe front focus problem when I bought it used. Canon fixed it for $200 and it worked fine with Canon lenses most of the time. After about a year, I upgraded from a Nifty Fifty to a Sigma 50mm 1.4 lens.
I found that the Sigma would front focus about 3-4 inches at full body portrait distance, but I liked the image quality enough that I learned to compensate by focusing on the model's ear instead of the eye. No micro-adjust on the 5D classic of course. The Sigma was my main lens for about a year.
Several months ago I bought a 7D and tried the Sigma on it, thinking that I would just dial in some micro-adjust. Doing some really precise testing, I did notice the focus shift with aperture changes, but it wasn't terrible. I decided to set the micro-adjust for the very slight back focus at f1.4 and ended up with only -1 compensation. Not bad, but obviously different than what I was used to with my 5D.
I put the Sigma away around that time, because both the 5D and 7D were now sporting zoom lenses. (Crazy focus stories on those lenses as well.)
Last week, while at a group glamour photoshoot, we were going to shoot with available light and I thought f1.4 would be perfect. I got out my Sigma and did some test shots with the 5D to see where it was focusing so that I could compensate.
I used a chess set in a "sun room" with large windows as my target and focused on the top of the white King. Magnifying the image on the LCD screen as much as possible, I was surprised to see that the Sigma was now focusing perfectly at f1.4. I shot two more times to verify and got the same results. I'll post one of these shots with a crop of the chess set. These are almost direct from RAW and my software applies minimal sharpening. Normally you would add a lot more.
If I had it to do over again, I'd probably buy the Canon 1.4 which at the time was $150 less, but I have enjoyed the looks I get from other photographers when they see that huge Sigma!
But my real point here is that focus performance is almost completely unpredictable due to the trouble prone system currently in use. It makes perfect sense to me that people on forums like this disagree vehemently about how well a particular lens or camera focuses. I think the system must have been designed in an era when it seemed that small aperture zooms would completely take over the SLR world. Those of us who choose large aperture primes are stuck with a lot of frustration.
Mike in Portland, OR