Suspicions Confirmed: The Summer, 2007 issue of The Upland Almanac has a one-page article by Terry M. Boyer entitled "Do We Still Need the 20 Gauge?" that is well worth your attention. The 16 gauge is his favorite because, as he says:
I have counted numerous patterns of one-ounce loads of different shot sizes out of different chokes in the 12, 16 and 20 gauge. The 16 gauge will consistently have a more equal distribution of pellets and a rounder area of impact than a 12 gauge. Twenty-gauge patterns are often elliptical, erratic and spotty."
I suspect his observations will confirm what a lot of readers on this web page already knew. But it's nice to have our experience confirmed once again.