Enya was the first to use AAC in mass production way back in 1974 with their 60X (also their first Schneurle ported). The Bluebird range (called Brat in America) from .21 to .45 were also AAC but for some reason their .51 is ABC. The Norvels were what was called AAO because they used an alloy piston and liner but the liner was plated with aluminium oxide which is otherwise known as a ceramic liner.

There should be no noticeable difference in power or handling between two identical ringed or ABx type engines but AFAIK only OS offer this with their ABN plane engines or the optional ringed heli engine. Talking about OS though, one thing I found interesting was that their top of the line Hanno Special started life as an ABN but later became a ringed engine with the Hanno II.

Given a choice, I'd prefer ringed unless it's for very high speed (20K+?) use where rings will start to flutter in the groove.