I've been using rtorrent for years and I wouldn't ever suggest anything else. It's just so damn simple and reliable. I love the concept of watch directories too. Upload a torrent file to a specific directory, and the data will be downloaded to a specific directory. You can have multiple watch directories for different types of data.

Note that rtorrent is no longer supported by homebrew[1]. You'll have to build it yourself with gcc since it can't be compiled with clang.

[1]: https://github.com/Homebrew/homebrew-core/pull/369

Transmisson can also run headless.