I have two each of MDT ACC and MPA BA Comp chassis. Both models are great; I like them about equally. I slightly prefer the MPA's grip arrangement, but the MDT's really long ARCA-rail fore-end has an advantage on some props. Six of one and half-dozen of the other.
But what sets the ACC apart for me is MDT's customer support. Nobody else I've dealt with comes close (well, Vudoo has been on that top rung). My few attempts at engagement with MPA resulted in, shall we say, not as positive an experience. Or there was no experience at all, if "experience" means a response to an input.
If you order an ACC and don't like it, MDT gives you a 30-day window to return it for refund.
I can't speak to other vendors' chassis. MDT has repeatedly earned my loyalty over the past few years, so I don't look elsewhere. My first MPA chassis came on a rifle I bought used from a buddy; I liked it and ordered one with my Vudoo. Then I tried an ACC; I liked it at least as much if not more, and my experiences with MDT support in terms of answering questions and working with me on a couple of magazine issues have made me a fanboy-level customer.
My $0.02.