They are two different rides. RnRC has a fast launch and upside down loops. Everest has only one large drop and no loops. RnRC has a shoulder harness; Everest has a lap bar. The roller coasters are very different on the thrill scale. I think the scariest part of RnRC is the launch; I personally don't find anything on Everest scary, but I would think the drop would get most people.
RnRC seems much, much faster, it's much darker inside, and has upside down parts and nice theming. Everest has a mean drop, a backwards part, and a two and a half ton audio animatronic. If you're scared of speed and loops, RnRC is scarier. If you're afraid of heights and Yeti, Everest is scarier.
Personally, I prefer Everest to RnRC. Mostly because the harnesses on RnRC are uncomfortable to me because of my... *ahem* buxomness.