QBittorrent
qBittorrent is a cross-platform freeware open source BitTorrent client developed to have the look and feel of μTorrent, without all the ads and bloat. The program is written in C++ and is simple to use and light-weight.
Personal
For a long time I was using a very out-dated version of μTorrent as my primary BitTorrent client because I didn't want to update to the bloated adware the program had become. I had tried other BitTorrent clients, but found them to be even worse. One day, I noticed in my list of peers that several people were using a client I had never heard of before called qBittorrent. I checked it out online and saw that it was built to be a free replacement of μTorrent, so I installed it and was impressed with it enough to switch over to it. It is now my primary torrent client.