Single rings seal effectively at high rpm, but not so good at low rpm. They offer less friction than a twin ring design, but also wear quickly if the ring is thin.
The OEM pistons are not a disaster, and they have long life, but if you're like me and OEM stuff leaves a bad taste in your mouth then fit the RM (or whatever) pistons. They won't be an easy plug and play, so be prepared for some cutting here and there.
If you want an easy life then fit the OEM stuff.