I don't have a lot of avocado greens, but I compared all three of them for you. Here's the cast of characters.
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I applied three coats of each, in the same order as above, from left to right. I took this picture in the sun.
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I took this picture in the shade.
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And I took this picture with the flash.
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The Nubar is the lightest of these three. It's also got the least amount of yellow in it. The formula is fantastic and if I'd been more careful, I could have gotten away with only two coats. It's the most pigmented of these three polishes.
The OPI and the Nina are pretty darn close. The OPI is slightly darker than the Nina, but I think they are so close that you wouldn't need both. The formula on these two is very similar as well. Both polishes are a bit streaky and watery, but look great with three coats.
I hope you enjoyed! :o)