rTorrent is a lightweight client running from the terminal. Being able to run it in a screen session (also upon boot) makes it ideal to also control it from a remote location.
Read it at howtoforge
However the current version provided in the ubuntu repositories is very much outdated. It's version 0.6.x – and features not yet encryption. So your ISP may throttel you bandwidth because of that. The version in the coming Ubuntu release is (currently) v.0.7.4. Also this version is already outdated. The current rTorrent release is v.0.7.8.