Best Torrent Client that supports auto unrar
Transmission is generally regarded as the best BT on the Mac, and can definitely do move on completion. That's found in the Transfers - Adding tab in Preferences.

It doesn't have auto unrar built in, but it can run a script on torrent completion.

There are several available scripts on the Transmission forums. Torrentexpander claims to work well on OS X and is written for Transmission.

As far as I can tell, the steps to using it are:


Unzipping it and putting the torrentexpander.sh file into a suitable folder.
In Transmission, open Preferences, and click on the Transfers tab.
In the Management sub-tab, tick Call script when download completes, and then point it to the torrent expander.sh file.


In theory, it should then Just Work. I've not tested it, but it's all free and worth a shot. Post back if you're successful!