Transmission: Amazingly simple, offers little customization, lacks support for DHT, but I still love it for it simplicity. Supports multiple downloads in one window.
Deluge: A bit bigger client, more customization, supports DHT. A bit unresponsive at times, I have had a few troubles with it in the past, so I do not use it anymore, but many people are pretty happy with. Supports multiple downloads in one Window.
Azeurus: Java based, meaning slow. I get the feeling you either hate or love Azeurus, I don't like it though.
rTorrent: Never used it, sorry..
KTorrent: KDE based, meaning allot of KDE libraries, but many use it anyways. I prefer a clean GNOME install though...
You're not drunk if you can lie on the floor without holding on.