I like Transmission. It's quite Mac-like in its interface and it gives quite a bit of control to the user. That said, I recently gave it up after hearing that µTorrent (also known as uTorrent), one of the premier clients on Windows, was finally available for Mac. µTorrent does use quite a lot of CPU, but the speed! I don't know if I'm just on popular torrents lately, but µTorrent seems to find a lot more peers and gets me a lot more download speed than Transmission ever did. Sometimes, download speed approaches what I get on the newsgroups. That increased speed is more than a fair tradeoff for the CPU utilization, in my view.