I have historically used the center point expansion but, after reading Artie Morris's guide to setting up your 7D, have been experimenting with the full 19 pt. focus that he often recommends. I have to say, it seems to be working out fairly well. All of the pileated woodpecker in-flight shots I got a month ago used it.
I also use the full 19 pt AF AI Servo, especially out in the open. The number of keepers are just as good and sometimes better than center point only. The only time I use the Center Point is if the background is messy.