Transmission, the lightweight, open source, and free BitTorrent client we've written about in the past, recently released version 2.0. Transmission was already one of the leanest BitTorrent clients on OS X, and the new version makes it even faster, with improvements to startup time, local data handling, and optimization of how you connect to peers and download requests. Transmission 2.0 will also search for and discover peers on your local network to connect with for even faster speeds.
While Transmission is a cross-platform, open source application, the developers continue to focus on making it feel like a native OS X app, and Transmission feels right at home with all of the other Mac-only applications I use every day. Mac users can now paste trackers into the Create window, magnet links will open the Add Transfer window, and the Compact View replaces the Minimal View to use less screen real estate.
Thanks to both its lightweight nature and its adherence to OS X design conventions, Transmission is one of the easiest torrent clients I've used. It accomplishes this ease-of-use without sacrificing the power features like scheduled bandwidth limiting, a Web interface for remotely controlling torrent activity, and port configuration; all of these features can be found in the well-organized Preferences.