The average person switching from Windows to Linux wants something that works. My general impression is:

- Anything other than Ubuntu and Mint requires involvement with 3rd-party repos for comparable multimedia playback

- Ubuntu has the largest userbase, and thus the largest access to easy tech support; a beginner isn't going to bust out Terminal and go straight to Arch wiki

- Because Ubuntu has the largest userbase, software is more tested on it; check the requirements for most games on Steam and most of them mention Ubuntu, or SteamOS; nothing else

- I remember years ago Debian having some confusion with different images and firmware. I don't exactly remember the problem (maybe missing firmware for netinstall?), but this wasn't an issue with Ubuntu that includes most of the stuff on-disc.

Debian feels like one of those barely-heard of distros. When I think mainstream distros for desktop, it's Ubuntu, Fedora, and openSUSE. For server, it's Ubuntu, RHEL, or SUSE. Arch Linux, Gentoo, Rhino, Cachy (or whatever it's called), Clear Linux, and Debian are distros to use if you have a known reason that they benefit your use case, after trying it from mainstream distros.

I wouldn't recommend Windows users to switch to any of those because of the lower user-base, and that because those distros are more technical there's also that air of harsh discussions and entitlement (Arch forums is terrible with this; RTFM). I don't know about anyone else, but I don't want my recommendation to be for anti-social entitled pricks who think they know better with their obscure distro :p If people want to go that way on their own, go for it!