I had the same choices as you. The pick from your pics are easy. Dolphin Grey for sure. The silver looks might blah, but that could be the light angle and base rims. Black would drive me to drink. And for A6's, blue, red and beige are ridiculously ugly.
For some reason, certain cars look great in one color and not so good in others. I almost opted for the Dark Grey but decided on the silver with black interior. Yes, the metallic silver doesn't give that ooh and ahh as black but the upkeep is sooo much easier and the silver looks mighty classy compared to straight white. Get the windows tinted (contrasts nicely with the silver) and 18" rims and you have a car that always looks good.
One hint on silver; keep the trim as dark as possible. The window tinting helped tremendously. Contrast is everything next to a light-colored car. So, keep the tire dressing up and the wheels clean.
By the way, in the early morning, dusk and night, the silver looks fantastic and the hood reflections while driving will give your detailing efforts more than enough applause. In direct sunlight the flakes will almost glow.
If you look at most Audi ads and brochures, the car color choice is usually silver--for what that's worth. The metallic flakes do pop nicely with the proper care--and that ain't hard to do.
Good luck with the selection.