As has been explained, ringed engines and ABC-type engine derive their compression in different ways. Ringed engines use a compression ring, while ABC-type use the differing thermal expansion rates of different metals to provide compression. Generally ringed engines take a bit longer to break-in, and ABC-type take a bit more care to break-in. Ringed engines have a reputation for long life. There aren't a whole lot of ringed engines made anymore compared to ABC-type.

Ball-bearing cost slightly more than bushed engines. They've got a ball-bearing supported crankshaft, and all things being equal will provide better performance.

Irvine, OS, and Thundertiger all make great engines in my experience. Irvine makes the best in my opinion, but they are a tad bit more expensive. Stick with a big brand and you should be ok.