Your skintone looks like my hubby's skintone, and he's half Irish! Does mom have Irish blood?
Here are some thoughts...
First, I think a 10 is not the same as a 20, so if you wanted to, you could get a 20 YG MOP also. They are very different looks. If I wore short necklaces (which I do not), I would have also purchased a 10 WG MOP, and I would wear it together with my 20 WG MOP to layer. I love that look! I do understand though if you want a different stone to have more variety.
That said, looking at your skin tone, I think it blue agate would be beautiful on you. Also, I think blue agate would pop next to that pale pink top in your photo. I love bright turquoise-blue shades against pale/blush pink (not bright pink). I know you said you did not like blue agate, but I have seen it, and it is mesmerizing. I did not like it at first. Perhaps it was because some of the earlier pieces I saw was blue with a drop of gray, and I thought it looked flat, for me. I saw the "new batch of blue agate" (my SA's words) a few months ago, and the blue agate was blue with a drop of yellow. It made the blue agate glow. As FYI, after I saw the recent batch of blue agate pieces in YG, I tried to put in my order for a WG blue agate set. My SA got an email from VCA saying they could not commit to making the 20 in WG blue agate. So... maybe try on blue agate again to be sure you are crossing it off your list just in case this stone may be hard to get in the future.
Assuming no to MOP and no to blue agate, my vote goes to oynx. I think it will look beautiful on you too, and it's very versatile. I do think oynx can be harsh on some skin tones. However, you are so nice and pinky and perfect for oynx. I think oynx looks great on pink skin as pink softens the oynx.
To help visualize oynx (black) in terms of clothing and color..
I think blush pink clothes look gorgeous with black. That color combo to me is the perfect combination and exudes "strong, feminine, elegance." Blush pink = you! Your skintone!
I think malachite would look great on you too although malachite in a 20 is loud, and I'm not sure how "loud" you like your jewelry (I love loud and bold).
However, you said you have malachite, so I assume you love that pop of color.
Malachite is a derivative from the blue family (blue+yellow=green). I am sure you love your malachite. Could you find some love for blue agate?
I really think blue agate would pop on you. You may find it pops too much though as a 20, and if yes, go with oynx (or MOP).
One final thought...
I'm a big fan of colored gemstones, and I think certain colors look better in certain seasons. Yes, you can wear jewelry year round, but for example, I have turquoise pieces (not VCA), and I only wear my turquoise in the spring/summer (I wear a lot of stripes and shorts in the summer). It doesn't feel right to me in the fall/winter and certainly not on a freezing snowy day as it is today (I wear a lot of black in the winter). Depending on where you live (do you have different seasons, mostly tropical, mostly artic) and how you dress (do you dress with happy colors, muted colors, black), you may want to factor these into your decision. You may decide you need more "summer jewelry" or "winter jewelry." I hope that made sense.
None of this may matter to you, and you just want to buy a color you love. I just wanted to share these thoughts to help you decide. For you, I vote blue agate or oynx. You can get the 20 YG MOP as your second 20 once you realize how goreous 20s can be!
I love 20s, they are so swingy and give off a carefree chic vibe. I think you will love it too! I hope that was helpful.
