Windows has an awesome and yet tiny BitTorrent client in uTorrent. Though there are many BitTorrent clients for Ubuntu, none of them come close. Of the lot, I have found Deluge to be excellent.
Deluge has almost all of the features present in uTorrent and has a similar user interface too. If you are coming from Windows, you might find Deluge to be a good choice of a BitTorrent client. The only feature I miss from uTorrent is the download and upload graphs, which surprisingly no Linux client currently provides! The rest of the features I used in uTorrent work in Deluge too: assigning ranks to torrents and priorities to files within them.
Deluge can be installed from the Ubuntu repositories by using the package name deluge-gtk:
$ sudo apt install deluge-gtk
Tried with: Deluge 1.3.5 and Ubuntu 12.04 LTS