The sad thing is back in the Windows XP days Microsoft had the focus stealing thing pretty much solved. Well okay - I remember you had to install some of the PowerToys or make some registry edits to get at some of the settings. But once setup pretty much nothing could steal focus away from the current window, which was a welcome change from where we had been. That started to break again in Windows 7, and has gotten worse with every release since then.
Admittedly XFCE isn’t perfect either, but it’s much better behaved than modern Windows.
I use BiglyBt on Debian. I use BiglyBt because I previously used Vuze, and I used Vuze because I previously used Azureus. I don’t really remember why I went with Azureus originally, but it may have just been because it was popular at that time.
I get the impression most people use other bittorrent clients nowadays, but BiglyBt does what I need it to do. I never really used any of the “advanced” features of Vuze myself, pretty much only using it for torrents.