Have you seen any of these bags in person? Fit is so important when it comes to the warmth of a mummy bag, its girth not being adjustable as is a quilt's. Since your clothing kit should already be pretty much dialed in before a purchase like this, then I'd recommend an in-store test if at all possible. Or order two, try them at home, and return one. As a general statement on design and materials, having seen a few bags from each of these brands, MH is out of its league compared to WM.
That said, at these temp ranges (and in the WM price range) I'd really have to recommend an arc-type quilt, Nunatak or JRB.