I’ve always pronounced it “di-a-beat-ees”
But recently I’ve heard a lot of people (esp. news reporters) pronounce it “di-a-beat-is”.
How do you say it? Which is more correct? The second version sounds very wrong, IMO.
My Webster’s says either way is okay.
As Chefguy says, they’re both correct, but I’m more used to hearing the former pronunciation.
Grandma alway pronounced it “sugar.”
Well, my brother has it, and he says “di-a-beat-ees”. 
(Or “sux-0r”, whichever).
I think the people who say “Dye a BEET ihs” are the same ones who prefer to call the Show Me State “Mih ZUR uh”.
“di-a-beat-ees” is the way I normally pronounce it.