qBittorrent’s strength is that it’s the most uTorrent-like client that isn’t uTorrent. Otherwise, there’s nothing really special about it.
rTorrent’s strength is mainly how lightweight and stable it is. If you don’t use ruTorrent, it can easily handle over 10k torrents. If you do use ruTorrent, it’s one of the most feature-rich clients out there (though it stops being stable around 3k torrents). The pyroscope fork is highly recommended — it’s more feature-rich, better documented, and the tui is quite a lot better.
Deluge is the most aggressive in peering. It’s the best client for racing because of this, but it isn’t as stable as rTorrent/Transmission and the plugins are not very consistent. Some only work with the wui, some only work with the gui. It’s pretty feature-rich but only if you can get the plugins working correctly. I’ve heard the max number of torrents it can handle is around 2k.
Transmission is lightweight, stable, and easy to set up. It’s one of the least feature-rich clients available, but it’s well documented and easy to write scripts for (easier than rTorrent, at least).Overheard by Greycoder 2019