µTorrent 1.5.437.
Unless you just love a huge footprint and java overhead, and messing with an endless multitude of pretty much useless poorly documented plugins, and enjoy restarting your client due to unknown causes of instability, and having to forward a TCP AND a UDP port (though that may have changed), then by all means Azureus will let you get your geek on.
Azureus also gets the nod if you want to set up a tracker on your PC although µTorrent can do that too (just with no interface to speak of), and who would when you can be tracked by Sladinki007 or Demonoid or the Pirate Bay or...well, you get the point.