I have a Kelly in VC Togo (GHW) and I love that color. Seems to work with everything and is just green enough to be seasonless. To me it is one of the newer colors that has really been embraced by H lovers, kind of a new classic.
Étain is one of those forever H colors and is a lovely, pretty much perfect, grey when you get the right dye lot. Since it sounds like you're buying at resale, you can see what you are getting, which is a blessing with this color. If it is a clean dark grey, then that is a very versatile bag.
If it were me, I'd buy the VC because it's a bit more interesting, but if you don't love green, it's not for you.
I never really understand the "holds its value" question, because buying a bag in the current market while already thinking about resale is an iffy proposition, and no one can predict what people in the next decade will want.
Good luck!