Depends on your coloring. Navy has dozens of different tones, to it . . . you need to select the right one, for your skin, hair and eyes. Same, with grey. There are blue greys, brown grays, black greys, beige greys . . . somewhere in there, you should find something that's right for you.
I'd argue navy with antiqued brass buttons if they have 'em. They're not so bright as to attract undue attention, yet keep the classic navy blazer look. What's your body type? I'm a big fan of hacking pockets, two button, and double vented myself, but it may require adjustment for you.
and I vote for black horn buttons. I think the horn buttons make the navy balzer a bit more versatile, like if you ever wanted to wear it with jeans. MTM is usually about a hundered bucks more than full price OTR. We are coming into the season where many retailers are hosting trunk shows with their vendors. Usually at a trunk show they will wave the MTM upcharge.