Yeah - it is complicated. I had never heard "sequel" till I started my first day job in the late 90's. But I swear the closer people are to databases management, the more I hear "sequel". SQL being spelled out is seemingly more people new to databases or used interchangeably like everyone has identified. I do say it either way, but I would always say "Sequel Server" for example.

I guess when I say "universal", I never hear someone say "what is that?" I mean - most programmers understand the term. I favour it as it seems easier to say.