I've been playing with both rings and cinch buckles the last week or so, although I've only been able to do backyard testing so far.
I haven't had rings slip yet. What I do is put a bight of webbing through on the last step. Gives the rings a bit more to bite on and makes take-down and adjustment even easier. It also means you don't have to feed the whole length of webbing through if your trees are close and small. What I don't like about the rings is that you have to be aware of how you're tightening to be sure the webbing stays in line.
I just got my cinch buckles last night and put them on my hammock. They're cool. You can still feed a bight through on the last step for easier take-down, but it doesn't seem at all necessary for security.
The difference in a pair of cinch buckles and four rings (two on each end) is 10g on my digital kitchen scale.
I'm still not totally convinced of full webbing instead of huggers/line because of the weight and bulk, but I do like the security and durability.