If you want to go purely by results, I think that over the past many years (10+), the top regions based on performance at L10 Nationals are Region 1, Region 3 and Region 5.
That certainly does not mean that there are not good gyms, good coaches and good gymnasts in other regions...there most definitely are. Chow's is in Region 4 and no one wouldn't say they are not a quality gym. Brestyn's is in Region 6 and they have 2 recent Olympians, Hill's and Parkettes in Region 7, so clearly these are great programs. For the national results, I think it's more based on volume -- California, Texas and the combo of MI/OH/IL provide a very high number of competitors and with that comes bigger gyms and places that high caliber coaches would gravitate to.
I don't think it takes anything away from anyone else to say that over this period of time, X Region(s) have produced the most champions....it's just statistics.