Shouldn't we rather celebrate the GA of Windows NT4 Workstation on August 24, 1996? It was 30 years ago and an amazing OS that at least for some tasks made me switch back from SuSe Linux.
Both are worthy of celebrating IMO. I had a coworker back then who got the NT Server tribal logo pattern tattooed on his arm.
Id say: both.
But yes, Win NT was the real game changer in Windows universe back then; if they hadnt made the switch, we would still have a tuned Win98/ME without proper multiuser account tenanting etc.