You can use virtualenv to manage the python version, also. If you have multiple versions of python installed, say python27 and python3, using the --python option of virtualenv you can tell it which executable you want to create the virtualenv with.

Honestly I always felt the various multi-ruby helpers were a bit too much for me. I just compiled my rubies my self setting --prefix during configure and then would just adjust a few env variables to set up things like PATH and GEM_HOME and had no issues.