My requirements were prioritizing, selective downloading, FOSS, a small footprint, and running as service/daemon, and I tried most of the clients on the Wikipedia list that fit these criteria. I liked Deluge most, though I still had a a few problems.
In the end, the problem solved itself when I did the switch from Windows to Linux as my main OS. I use rTorrent, daemonized in screen now and have never looked back. It's very small and has console and (optional) web interfaces.
Oh, and please don't tell anyone I said "FOSS-software".
computers are not able to distinguish between a paragraph of As I Lay Dying (William Faulkner) and a gallon of sophomoric babble
Then I'd say they're pretty accurate.
Real Users find the one combination of bizarre input values that shuts down the system for days.