Deluge is one of my favorite BitTorrent client that uses LibTorrent (BitTorrent library written in C++). Deluge is implemented to use the client–server model and a daemon process that manages all tasks related to bittorrent.
Deluge has an interesting collection of features and functionalities, and it is designed with the intention of being lightweight and consumes less system resources so as it does not interrupt other running programs or activities. Deluge runs perfectly in KDE, GNOME, XFCE and other desktop environments.
To install the latest version of Deluge (currently 1.3.3) on Ubuntu 11.04, run these commands via the Terminal:
sudo add-apt-repository ppa:deluge-team/ppa
sudo apt-get update
sudo apt-get install deluge
You can then start it via the dash (Unity):
You can really use Deluge as your default bittorent client under Ubuntu due to its simplicity and ease of use. As stated by the developer, this bittorent client is created to be unobtrusive and not a resource-hungry application.