When I first came to Linux I adopted Transmission. It seemed less featureful than others but now I like its simplicity, does everything it needs and it is also very reliable.
It is not very known but there actually is a transmission-cli for common torrent operations that may come in handy some time.
There's also the Transmission Remote GUI, which is a nice GUI for remotely controlling the Transmission daemon, on say, a NAS: https://github.com/transmission-remote-gui/transgui
It's great for keeping downloads going overnight without having to leave all the power-hungry devices powered on.