I say Ee-En-World (since they were initials), so I've been saying Ee-En-Sider.
But I could also say Insider, like the the actual word. I do say Ennies as Innies, after all.
Or, I could try to actually say the the "five" in the word, like Ee-En-Five-Eye-Durr.
I know it really doesn't matter...