I'm a 90s kid from southwest Germany and never noticed the console wars. Nobody I knew owned a Sega console here. It was NES, SNES (and some C64, Amiga) and later mainly PS1, PS2 (with N64 and GameCube being less common) that everyone owned. This is just from my childhood and other kids I knew.

I never saw a Sega console in the wild here. From talking to other people online it seems Sega was popular in the UK, but not here. It'd be interesting to try and get memories of folks from different European countries for comparison. I can't comment on the USA of course, the gaming market was probably way different there.

As for Nintendo and Sony, if there was a rivalry in advertising I didn't notice it. For the most part people played whatever console they grew up with although I'm sure many switched from Nintendo to Sony as they got older. I remember the kiddie image for Nintendo was prevalent, Sony had games that appealed to older players. By the time I started using the Internet in the early 00s the console wars had already died down.

Personally I've never had any "mine is better than yours" discussions with friends because the games we had on our consoles were different. I was an N64 kid but often played PS1 (Crash Bandicoot, Rayman, Pandemonium) at a friend's house and enjoyed it. And we had many great multiplayer sessions (Mario Kart 64, Mario Party, Banjo-Tooie) with the N64 at my place. It was just a different console, there was no rivalry mindset with us kids.