>why would you go FROM Transmission to qBittorrent?
In my case: some torrents wouldn't find known-good seeds in Transmission but worked fine in qBittorrent; there's reasonable (but not perfect) support for libtorrent 2.0 in qBittorrent; my download speeds and overall responsiveness is anecdotally better in qBittorrent, and; I make use of some of the nitty gritty settings in qBittorrent.