Those 2 are from actual small mills that stone grind their grits. The others listed are commericially available products that sell on regular grocery store shelves here and are mass produced, not stone ground and not nearly as good.
I tried to find a site that sells Suber Mill Grits. Those are THE best. We can get them at the local farmers market. They not only grind their own, but they grow the corn too. I haven't been able to find a site that sells them over the internet.