I've used a Humanscale Liberty chair for a full year now. Here's what I can say:
1 The back mesh is great. It really conforms to my back and is just enough support without any foam. 2 I love the smooth seat slider and arm adjustments that allow my wife and I to quickly and easily change the chair's dimensions. Important for us, since she's 10 inches shorter than me :-) 3 After a full year of nearly daily use, the chair still feels rock solid.
Looking back on my purchase now, I'm certainly glad I chose the Liberty. And I suspect I've got many, many years of comfortable sitting ahead of me.