Another vote for B+W. Except...you mention grad ND, and for that I'd skip round filters - that forces you to have the horizon in the middle, and compositionally that's rarely where you want it. Schneider Optics (parent company of B+W) makes excellent rectangular glass grad NDs in their MPTV (motion picture / tv) line, or look at Lee resin filters. You can either get a rectangular holder, or just handhold them.