What I do know is that for a period of time I was on a mad chair hunt. I went from store to store trying to find that perfect million dollar chair that would stop my legs and feet from hurting due to lack of circulation because of how long I'd sit for.
In the end, after sitting in Aeron after Aeron and others, I gave up, realized every one of them was a waste of money.
The solution was cheap and simple:
1) I kept my cheapo $70 chair from Office Max
2) I put a $90 cushion on it (one of those you can carry with you and put in your car).
3) I put a wooden tangerine crate inside of a cardboard box, taped it up, and used it as a foot support to elevate my legs, thus relieving pressure on them from the chair's cushion.
That's it. I was able to code much longer now without taking breaks, for a fraction of the price. Then again, if you're buying for other people, this sort of setup might cause them to roll their eyes, this is mainly just advice for people looking to buy chairs for themselves.
Of course, don't forget to take periodic breaks and exercise. No matter how expensive or ingeniously setup your chair is, unless it's levitating you in the air with force perfectly distributed on every square inch of your body, you'll need to take breaks to allow your blood to circulate properly.