Nearly every time I mention anything having to do with BitTorrent, I receive at least one comment from TUAW readers insisting that Tomato Torrent is absolutely the best bittorent client for Mac.
Well, there's a new version, 1.1.2, available today, so I thought I'd mention it. One of the reasons this BitTorrent client is so highly favored on the Mac is that it separates "the BitTorrent code from the Macintosh code, so that either can be updated without having to modify the other." There is no java involved, as with Azureus.
Tomato Torrent is based on BitTorrent 4.0.1 and is AppleScript-able. Check it out.