rvm hooks into the cd command which has caused people nightmare-level debugging marathons. rbenv's key feature was that it did not do that and uses a shim instead.
To add a little more to the history, I made the switch from rvm to rbenv when rvm broke under me (I can't remember now whether it was `cd`-hooking or rubygems-bundler which broke the camel's back). I made the switch from rbenv to chruby when rbenv's shims broke. Chruby does so little that there's almost nothing to break, so I've stayed there.