I owned a lot of different chair: the aeron, the vitra headline http://www.vitra.com/en-us/office/products/headline/overview... and quite a few grahl duo backs http://www.backinaction.co.uk/grahl-duo-back-chairs but the very best office chair I've owned and use daily is the "loeffler ergo hocker" http://www.ergowebshop.eu/Loeffler-Ergo-EF-9150 it's an amazing stool (I actually bought three of them, office, home and an older version I gave my brother) it's the only stool I've used you can actually sit on all day long (I'm a coder) without noticing it, the design makes sure that you keep moving without it becoming annoying. And it's cheap! (relatively ;))