Upload & Sell: On
If you haven't yet, take some time to read the "Autofocus Reality" blog posts by Roger over at lensrentals. This is the summary post: http://www.lensrentals.com/blog/2012/08/autofocus-reality-part-3b-canon-cameras
It's interesting that the 5DIII, and likely the 1DX, performs consistently better in terms of AF accuracy than older Canon cameras, so obviously Canon has made considerable improvements to the latest AF system and most recent lenses. And it would be interesting for Roger to repeat this test with various Nikon cameras and lenses...
Regarding Canon vs. Nikon, it would seem, at least in the 5DIII and D800 camera class, that one has to prioritize the importance of certain features. I.e., is AF precision/accuracy/consistency more important than a banding-free sensor with more shadow recovery latitude? After dealing with Canon's backwards AF performance slide in the late 2000s, it's great to see the latest system is once again looking to be best-in-class. Unfortunately it means spending money to get it...
Roger's series is great and he plans to repeat the test on some Nikon bodies as well. I suspect the Nikon bodies will do about as good (or bad?) as the pre-5DM3/1DX results. It's a not-so-well-kept secret that Phase Detect AF has not been up to the task as of late, esp for the higher density sensors. The 1/3 stop margin of error that is usually quoted is just not good enough for large aperture shooting. Before the 5DM3/1DX there was no body that could consistently focus accurately for medium-to-long distances at f/1.4 or f/1.2, and this unfortunately includes the D800 as well. It's telling that Canon is not talking much about the single-shot AF accuracy improvements of the 5DM3/1DX + newer lenses, as doing so would be admitting that the previous system was underwhelming. With Roger's help we're finding out that Canon is doing a silent upgrade to the entire system. Hopefully Nikon will as well.