If I have free bandwidth, am I better off sharing as a relay node or exit node?
Trying to help the Tor network
Tor need more Relay Nodes, you also can modify exit policy to not open Websites and SSL.
There is the guide how to configure tor as relay via user interface Vidalia:
From their site, they appear to be specifically interested in adding relay nodes.
https://www.torproject.org/getinvolved/volunteer.html.en
there are probably people you can contact via the volunteer page to ask any further questions you may have.