qBittorrent if you want a drop in replacement for uTorrent, otherwise Transmission is great if you want it running in the background and like having some command line control.
It [qBittorrent] is ugly as sin and there are also a few hoops to jump through to get rid of OSX's "Allow qBittorrent to accept incoming confections?" alerts. But I've found it rock solid and more reliable than either uTorrent or Transmission