Herman Miller Aeron for example is great for people who are either small or sit "correctly." If you fold your legs under yourself, it is super uncomfortable.
My finalists were the Aeron, Embody, Steelcase Leap, and Gesture. The Leap and Gesture worked much better for my lazy ("natural") seating position. I ultimately purchased a Leap because the Gesture's arms shifted every time I stood up, and weren't as supportive.
Also our local dealer matched a major online dealer ($150 off).