I agree with john5189. I generally select the center focus point with the four expansion points active around it. If my subject is off-center I'll select a different focus point using the joystick. If there's a lot of "stuff" around the subject I'll use spot AF. I haven't tried zone AF, since, as john5189 says, that will result in the focus point in the zone that can acquire focus on the nearest object taking priority, and the nearest object may not be what you want to focus on (for example, a stick on the ground might be the nearest object within the selected zone - the actual focus sensors cover a lot more area of the scene than the focus point boxes in the viewfinder, so just because something's outside a focus box won't keep the camera from focusing on that something if it has a high contrast edge).
I would not use a zone AF selection to shoot a group of people. If I'm shooting a large group of people the most important consideration is probably not the AF point mode but instead ensuring the f-stop is adequate to get enough depth of field to get them all in focus. You mentioned that in your post, but I want to reinforce it here because it's a lot more important than which way you set up your AF focus points. You will get great results using center point AF as long as you have sufficient depth of field. For example, if you have a group of people and shoot at f/1.8, with any normal focal length and shooting distance you're not going to get them all in focus no matter what AF point selection mode you use or where you focus. If you shoot at f/8, you'll have a lot better chance of getting them all in focus regardless of which person you focus on or what AF point selection mode you use.
