The two are very different colors, but it think your dilemma is about the two being two neutral colors. Am i right? If that is what your main concern is i will advice you this. First of all, are you planning to collect birkins? Meaning do you wish to own a lot of birkins? If your answer is yes, then you should get it as the two colors are very different.
However, if you are planning to own just a few let's say 2 or 3 pieces, then i will advise you to buy brighter color.
As for myself, i do not plan to own tons of birkins. To me 2 birkins are enough and i will get one neutral and one of a brighter color.
Good luck deciding
I have a gold birkin, and etoupe Constance. They serve different purposes, and I love my neutrals so it works for me.
I agree with other posts. If you intend to have several birkins and/or love neutrals, get both. If you are only going to have 2 birkins, I'd pass and get a pop colour next or darker neutral such as graphite or indigo.