HELIOPAN OR B+W
Not ND, but in this test of Polarizing Filters Heliopan didn't do so well. B+W (sort of ) came out on top and Marumi were surprisingly good.
I disagree with this test results. I have both the B&W and Heliopan polarizers and cannot see any difference in their quality apart from the fact that the Heliopan filter is a little bit warmer than the B&W, and it's a little heavier (more solid frame).