Well I'll weigh in here by saying my personal preference is for a ringed engine (given the option). I'm not concerned about the longer and more critical running in required because I value the longer life the far more dirt tolerant rings will give and then the far cheaper cost of overhaul when it's needed. On that point it should be noted that where you can just buy a ring by itself, you can only get a matched ABC piston/liner because they're not available seperately.

One area where ABC is better though is at extreme high revs (20K+) because rings can start to flutter which wears out the ring groove. Piston drag (friction) is virtually the same though no matter what type of set up is used because all drag comes from the parasitic drag of the oil film and not metal to metal contact. Any additional drag (enough to noticeably reduce power output) would be converted into heat and yet both ABC and ringed run at much the same temperatures.

I guess what it comes down to as far as the original question goes is that if you're a typical modeller who just wants to get out and fly with the minimum fuss and buys a new engine because the latest one is a different colour then an ABC will suit perfectly.