I used µtorrent. I used to like it more in early versions. It used to be micro with lots of settings to make it behave exactly like you want. It has all the features but now its a bit annoying with its installer. I preferred the stand alone windows version.
Transmission is just a dumber more basic torrent client. Fire and forget style. I never liked it. Once you are used to something like µtorrent, transmission is just not an option.