uTorrent FTW
I don't consider closed source clients for security reasons, or bloated ones (Vuze etc.) because I'd rather use a spare GB of RAM to make a filesystem more snappy than to load a Java environment that eats alone half the resources of a small server.
Deluge is more of a power-tool, albeit one most people can use happily.
The big thing that I like is that you can use the desktop GUI (GTK) client with a remote daemon doing the actual downloading. Plenty of them have web-clients (Deluge does as well), but it's nice using the proper GUI. Other than that, it has all of the usual tools you'd want from a client.