I would totally get the HD800 personally, and did. I am satisfied with my choice, though right up until I bought the HD800 I had determined that (price being equal) I wanted the open Ether more than either of them, based on listening.
I feel like the HD800 does soundstage size, positional imaging, and comfort best. They IMO do a very good job creating a speaker-like experience (without extra bass). There are also smoking good deals on used ones. I decided those things were what I cared about most long-term, and I happen to own an amp (liquid carbon) that I heard and felt was a great pairing with the HD800 with none of the fatiguing treble I'd heard others complain about.
I personally feel like the Ether C is better for privacy, concentration, and "fulfilling what headphones do best." That last comment may be confusing, but if you think of all the reasons why you would choose to listen to headphones instead of speakers, then I'd say the Ether C does a better job responding to all those reasons.
In the end though, (almost) all the headphones at this price level are incredibly great, and if you can afford it, either one of these is going to be a very impressive and satisfying headphone! You should pick based on which appeals to you more, and then feel content because you won't be making a mistake