Non ringed engines usually have larger port area because there is no concern of a ring getting hooked in a large port. As a result, they can make a bit more power.

The down side to non ringed engines is the cost of replacing the piston and liner when the engine tires, versus simply replacing an inexpensive ring.

On the other hand, non ringed engines do not need extensive break-in time. Ringed engines do.

I run both interchangeably. To me, both have advantages and disadvantages, making them about even in the end.