Truth be told, I have never been comfortable in a normal chair, sitting still, two feet on the floor. It's so confining and conformist!
I am more the cross-legged, both feet under me, one leg under me, one-leg-sprawled, feet-on-the-desk type. I thought I might outgrow that and learn to sit "properly", but I don't see that happening. Currently I alternate between a cushioned backless stool (to my left) and my very attractive decor-matching stability ball. It's just enough freedom and movement to keep me happy.
I personally couldn't work at a treadmill desk, nor would I want too. I like to keep my work and workouts separate. Plus my keyboard is not sweatproof.
Remember those kneeling chairs? Those didn't hang around long.
Then we have the lazy options. Why deal with all the hassle of actually standing on your own when you can have a chair do it for you? Supporting your own bodyweight is SO overrated!
Then why sit when you can lounge?
And for the really lazy....or overtrained. Now THIS chair has some promise!