"What is AMA?
AMA is short for Advanced Motion Accelerator. It' new technology to give greater voltage to liquid crystal, BenQ improve the gray to gray response time and image became clearer and more vivid."
Source: http://www.benq.com.au/support/
So, if you want clearer and more vivid picture then turn it as high as it will go...at least in theory. I would honestly change it depending on the game. When you start up a game then toy with the option a bit to see what looks best for it. It is just like the contrast, brightness, etc. settings that a display will have...depending on the particular game, sometimes those settings need a little tweaking. So it is all subjective to a point. Hope that helped a bit.