Torrent Software

ruTorrent

• ruTorrent seems to be the best choice so far. Good web interface (native), lots of options. It is available in Gentoo, although the GUI must be downloaded separately. Update: it's now available in Portage, but I did not check it.
• There is no init script available, so best way to load rTorrent is to run in a screen the following command:

sudo -u torrent rtorrent

then detach the screen.

Deluge

• Deluge is an interesting choice, but not very stable nor fast.

Vuze

• Vuze has a buggy and outdated web interface, mostly because it is written in Java (applet). On recent versions, it does not work at all. Not a good choice for a server.