I love my Allsteel Acuity chair which has a mesh back and a firm and not too plush seat. Armrests adjust up/down, side to side and the whole thing oozes quality.

I used to use those cheap vinyl office depot chairs and they are just too plush to be good for extended sitting periods. They also tend to break down after a while.

In our office, I bought a ton of used high end furniture from a dealer in San Jose who buys them from Apple/Cisco, etc. when they upgrade. We got everything for about 20% of original price and they steam clean and delivered to our office. We're using Knoll Life chairs and a mix of Herman Miller Mirra chairs, both of which I like a lot.