What port do I use for downloading bit torrents on my Mac?

I believe which port really doesn't matter, but you should make sure that the same port is reserved through your router, like in Azureus preferences --> connections , just make sure that the port number listed there is reserved in your routers options as well, this will ensure that no other application is using this port, or stealing it's bandwidth. Hope this helps.

You might want to give Transmission a try. I think it is the best client for OS X.
http://transmission.m0k.org/

And really, if you use a router make sure you forward whatever port you are using for Bittorrent. See portforward.com for directions..
http://portforward.com/english/routers/port_forwarding/routerindex.htm