There is no comparison in glass quality IMHO. The Gen II razor is leaps and bounds above the mark 6. I've owned both and hated the MK6. Was the most infuriating scope i've ever owned. Glass was subpar for the price, clicks were mushy as hell (M5B2 knobs), tracking was 2/10ths off at 10 mil, and the eyebox was to date the most sensitive i've ever been behind. Supposedly they've fixed a lot of these issues with the Mark 5 which i'm eagerly awaiting reviews for.
The only real downside to the Gen II is the weight. It's glass is far superior in terms of resolution, CA control, and low light to the Mark 6. They're just a total pig of an optic. If you're looking at retail i'd just jump to the AMG or wait and see how the Mark 5s pan out.