What are the best ergonomic chairs for people who hunch their shoulders?

Any chair that has a firm back and firm seat with an adjustable lumbar support would be a good start.  Many chair companies will say that their chairs are "ergonomic", but it depends on how you feel sitting in the chair.   Cost is also a factor.  I wouldn't go too crazy in terms of really expensive chairs because, in my experience, expensive doesn't always equate with quality.  Make sure when you are fitting yourself to a chair that the seat depth is such that your thighs are supported and your feet are flat on the floor.   

As for hunching of the shoulders, this is something that can addressed with exercise (i.e. shoulder blade pinches) and being aware of your posture.  If you find yourself slouching or hunching, put your hand on your chest and raise your chest into your hand without taking a deep breath.  This will help to right your posture.  If you do this and are aware of your posture, you will eventually fix your posture automatically and not even be aware that you are doing it.