I've sat in the Herman Miller Aeron chair and the Steelcase Leap chair, and I still like the Freedom the best. I prefer the model with the headrest because I am a tall, big person. The freedom high back offers me the most support out of all the chairs I have tried. I definitly recommend this chair to anyone sitting for more than 3 hours per day. You will feel the difference.
Humanscale Freedom Ergonomic Chair 
