I switched from Transmission to qBittorrent a while ago, and I have some regrets: mainly that the qBittorrent web ui is extremely hard to navigate on mobile. Everything is tiny, and I can't zoom in and navigate around the page without right-click menus popping up
If you use the 'arr suite of software, NZB360 is invaluable for controlling them from android.
Sonarr, Radarr, Lidarr, Prowlarr, your torrent and usenet clients, as well as any web app you want to add, all in the same place with a really smooth interface.
It even combines the release calendars from them together into one. :)