The following article by a good pt discusses what types of chairs are good for what types of back problems and how to fit chairs to a patient
Once you understand the principles, I think it's easier to get a chair that works for you.
The thing is there is no one best chair, it depends on your specific back problem, what you do while sitting, and your dimensions.
This store fit me to a chair and it's the only one I sit for any length of time.
Eileen Vollowitz. "Furniture prescription and the conservative management of low back pain"
http://www.backdesigns.com/AB1921000...nrx.pdf?SID=1&