I use Flud for torrents, it works very well. Good interface and has all the functions. Also it's faster than uTorrent on my mac.. as fast as Transmission. it's free and there is no need to upgrade to 'pro' version because it has only a small add in a corner that covers about 2% of the screen.
and as a tip one thing that I noticed with torrent clients on the gt1: even if you give them permission to download to an external drive they actually download it in the default location then they move the file [which takes a lot of time and it's prone to errors especially if you download something with many files like tv series]. it's better just to make a Movies folder in their default download folder and add that folder to favorites in kodi.