I use to be a big fan of uTorrent 2.2.1 (was never a fan of uTorrent 3.x and its ads) but then recently I had issues with it grinding my PC to a halt. It would monopolize the drive completely, not writing mind you, just prevent anything from access for a time. Now, this wasn't an issue when I had a dedicated drive for incoming files, but when I had to move that to a partition on the windows drive, it was hell.
Anyway, Im currently using qBittorrent, its like uTorrent but purple. Oh, and it doesn't monopolize my PC and lock up everything like video playback for a time while downloading... randomly. However, I think it's not as good at seeding. I swear I had more uploading going on while using uTorrent.