If I had to guess, the most per capita would likely be in PA.
As to growth, I think a lot of that would be a function of where people moved to, and at one point, Florida - with its abundance of retiree related parish growth - may have been said to have been the most "growing" in the sense of new builds... but a lot of that was a function of "migration" of a sort.
A few years back when my priest was on vacation in the Sunshine state he concelebrated at a "new-build" UGCC parish that was only a few years old (if that) at the time. The parish population was largely (at that time) comprised of Canadian retirees who were refugees of the Canadian snow!
I am not certain of the demographics of growth if you are meaning "conversions" and young families. For a time, certain of the California parishes filled up with some Romans who (in retrospect) seemed to be "cooling their heels" in Byzantium - when the Summorum Pontificum came out liberalizing the old Latin Rite - which a lot of our visitors seemed to have a preference for - came out... Well a lot of folks seemed to disappear.
The Eparchy of Van Nuys has experienced demographic decline with the matter of "visitors going home" perhaps having an appreciable affect.
