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.

DHT

• DHT allows trackerless torrenting, ie peers connect directly to each other without the supervision of a tracker. Most private trackers disable DHT in their torrents, but it can be useful for random torrents found on the Internet when the tracker is long gone but peers are still seeding the file.

• On ruTorrent, DHT is disabled by default but can be activated using the web interface easily.

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• Vuze has a buggy and outdated web interface, mostly because it is written in Java (applet).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.