Violet. I had a Vert Deau City that I never carried so I sold it to a friend that had always loved it. But now she has changed her mind and is now selling it! I think you'll find that the Violet will go with so many things. I never loved my Vert D because it ended up being too pastel for me. I think most people will vote for Violet too!
I say Verte D'Eau. I finally got one and I find it goes with more than I thought it would. The leather is gorgeous on every Verte D'Eau that I have seen, not so with Violet. If you can, get both. It may be a long time before they make another purple but on the other hand if it sells well this season, they do seem to be repeating similar colors much more frequently.
I vote for Violet. Bear this in mind though, if this is a bag that you will be using quite a lot, go with the Violet, if this is a bag that you will use when the urge strikes you, then go with the Vert D'eau. I think that in the long run, Violet is going to wear far better than the V D'eau. There have been posts about the V D'eau fading and yellowing with time, not so with the Violet.