Originally posted by Fat Albert Is there a good reference online that explains the nuances of these different AF sensors?
That would be fantastic, but I don't think it is available in any one place. We have seen various threads, especially among the B-I-F shooters. They seem to prefer nine-point focus, and that stands to reason. Keep in mind, to clarify what Adam noted, that nine-point can be shifted somewhat to the various zones. I'm yet to hear of any advanced users recommending the "automatic" mode for any reason. It seems that most folks prefer to select the exact focal point, whether center or not. I tend to agree with those who have indicated that the nine-point zone (centered or not) does not do a great job of figuring out the desired subject. Still, I think it is probably the best setting for most sports shooting involving a number of subjects.
Ultimately, it takes some playing around with the various modes to get a good idea of how the metering modes perform. You also have to adjust the various menu items pertaining to focus-confirm vs. FPS-priority (focus-confirm is generally preferred, Auto is not terribly functional), and the extent to which a moving object is in "Focus-hold." The general consensus is that using the back button AF exclusive of the shutter release (AF2 on the menu) is preferable - and I'd agree with that.