Laanguy,

The TBO (Time Between Overhauls) for an ABC engine is the longest, but a ringed engine is much cheaper to overhaul, given only the ring has to be replaced.

The ABC is usually more powerful, but I cannot tell you by how much.

ABC engines need a short, rich, two-cycle break-in, at running temperature. The ringed engines need a much colder, four-cycle rich initial break-in, with a rich, two-cycle continuation.