I'm a relatively hardcore Azureus bittorrent user. It's the gold standard and there are a lot of resources for how to use/configure the client.
That said – it isn't very "Mac-cy". So, with some fears that I'm trading style over substance (yikes!), I'm kicking the tires on the Xtorrent beta.
After a little experimentation – Xtorrent is defintiely substance with style.
Besides being a robust BT client, Xtorrent has built-in torrent search capabilities. You can confirgure the engines/search sites to your liking in the preferences menu. It adds iTunes-like filtering to the search results. Just hit the "Download" button, and off you go. Xtorrent makes BT easy, and -hopefully- that will mean more seeders, definitely a good thing.
You can also easily configure Xtorrent to store completed downloads according to content. For example, Xtorrent can store a movie in the Movies folder, or load music files directly into iTunes. Sweet.
In running Xtorrent side-by-side with Azureus, I was getting higher reported download speeds with Xtorrent. (Not sure how/why, but, it is what it is.)
The one (BIG) drawback is that it doesn't seem to have encryption support, at least not yet. The encryption plugin for Azureus is a must-have, IMO. Another drawback is that it appears to lack of the ability to download just certain pieces of the torrnet. So, if you're downloading music/movies, getting just one song or a sample file is likely not an option with Xtorrent.
Anyway, if you need a simple, straight-forward BT client with Mac style, check out Xtorrent.