I honestly don't think it matters how you say it....

I say Eye-ko even though I know Japanese and know how to say it as it is written in Katakana.

Ee-ko ;)

Eye-co

I've always thought it was EE-ko since I heard about FFX Tidus is pronounced TEEdus.

Wikipedia is useless.
Ive never, ever heard anyone pronounce it ee-ko. Even when other industry people discuss the game, its Eye-Ko. If you think about it, it has the same structure as the word Icon. Take the en sound away for the lack of an N, and you have Ico - eye-ko.

However granted, that the I sound in Japanese is often pronounced with an Ih sound, it might actually be Ih-ko.

Ik-ko.

@ bardicverse )

"eye-ko" is likely the natural way of saying it for people from english speaking countries, but in many other languages (like for example my mother tongue, german) I is pronounced "ee"

eye-ko

As I speak spanish and I know the word comes from japanese, I say it as it would be pronounced in both languages (the correct way), "Ee-koh"

For those who are still in doubt, the katakana gives the way to pronounce it: イコ is pronounced "ee-koh". If it was to be "eye-koh" it would be written アイコ

ais-ko - I was way off