I always pronounced "Mah-ko" as well. But that's mostly because in my native language we pronounce the "A" like that all the time. --- Is that a hobbit?...No,that's a hobo and a rabbit..............but they're making a hobbit.
Mah-ko. In the japanese version, it's actually written in kanji (actually, I believe you can also see this somewhere in the US version, maybe the vehicle demo inside Shin-Ra Bldg.?), so I assume it's an actual Japanese word.
PS: the "Mako" in Mako Shark is also pronounced mah-ko.
It's mah-ko, if it was pronounced may-ko it would be spelled meiko. But I like the may-ko pronunciation better. --- If you had told me 5 years ago that I could play Spyro the dragon and Final Fantasy 7 while on the toilet, I'd have said you were mad. And then god gave us PSP.