Steelcase Leap. Similar to the HM Aeron, but has cushion instead of mesh, and offers a bit more adjustment. It comes down to a matter of personal preference, but many prefer the comfort of the cushion. Personally, I sometimes sit with a leg crossed under me, or sideways in the chair, just because I like moving around, and the Leap is comfortable in all positions. Before I purchased it, I was having horrible wrist and shoulder pain, but it vanished once I swapped to the Leap. I've owned mine for a few years and it still looks pristine.

I also bought it on Craigslist for $200 brand new, which was quite a steal.

The Leap and Aeron are among the best in class, and it's hard to go wrong with either. Go to an office store and try both for yourself.