I've had my Air Flex for about two months now, and it is pretty good. It isn't the absolute best girth, but it is better than a lot I have tried.
My horse sweats A LOT, and when I would untack him, even after a short ride at a walk, he would be soaked under the cinch. Now that I have switched to an Air Flex when I untack him, he is only slightly damp (what it should be like, not soaked) even after a longer ride with lots and lots of trotting.
I would recommend the Air Flex, but I really haven't used mohair so I can't add to that. It is pretty reasonably priced (cheaper than nice mohair, which is why I bought it as my parents made me pay for it) and I would say worth the money. Haven't had any problems, no rubbing or irritation. I am only a "casual ride", not much longer than an hour or two 3-6 times a week and no showing/working so I don't know if that plays a role either.