I have used first Turbo Torrent. It`s good program, but last version is very unstable and crash often. I have used BitCommet, G3, BT, Rufus, ABC, XBTT... Now I am using Azureus. It`s the best torrent client who I am used. Works stable, has a lot of features, useful plugins and nice easy to use interface. Azureus is my number 1!