Funnily enough, my experience is a combination of both yours and the GP’s. MSN Messenger vs AIM was what I perceived as the first big megacorp battle on the internet with ads everywhere and it was the first set of platforms people just had to be on. That’s when the internet went from IRC/BBS/small forum communication for nerds to my non-technical school friends using it.

The cool kids (nerds) later just used Pidgin or whatever, but I remember that era as being the first intense competition over the internet. Probably says more about my age than anything else.