Hi! If you can 100% wear the blue agate often, yes, it adds a nice pop of color. That blue shade though to me is hard to match, and I personally do not like it with navy or black.
That said, I vote MOP. Why?
Yes, the blue agate color pops, but I think it looks busy with your stack. Your stack is already a very busy stack, and I think the MOP goes better with it as it creates a more pleasing flow to the eye. The blue agate takes away from the overall stack theme in my opinion and makes it look like you just added a color, for the sake of adding color. Imagine if that blue agate were just a blue bead bracelet (non-VCA), would you still like that blue on your stack?
With the MOP bracelet, the eye can gently scan across all your bracelets.
With the blue agate bracelet, it screams too much and is a very sharp contrast to your other gold bracelets. I find it detracts from the rest of your stack.
Finally, if one day you decide you are sick of so much stacking and want a cleaner look (and you will, promise), I think the MOP and hammered gold go beautifully together. It's very elegant and timeless.
MOP also just makes the skin glow. The iridescence is beautiful.
Just my two cents for another point of view. Hope that helps.