I know I am an outlier, but to me the only rule that matters in an RPG is how to determine if a character succeeds or fails at any given task. The rest is all chrome and fluff beyond that. Therefore, this mechanic or system needs to be rock-solid in order to have a successful RPG experience.

That being said, what are some of your favorite resolution mechanics for RPG games with GMs?

I have a few biases is this regard, but would love to hear some of your favorites before I jump in.