qBittorrent is probably the most actively developed Linux Bittorrent client, with new versions being released constantly fixing lots of bugs but also adding nice features to make you forget uTorrent is coming to Linux. But actually qBittorrent is not just for Linux anymore: recently the Mac development started again and it is now also officially available for Windows too.
qBittorrent 2.2.10 was released today bringing lots of bug fixes so it's advisable to upgrade to the latest version. In Ubuntu, you can install qBittorrent using the following PPA:
sudo add-apt-repository ppa:hydr0g3n/qbittorrent-stable sudo apt-get update && sudo apt-get install qbittorrent
For other Linux distributions, Windows and MacOS X, see the qBittorrent download page.