As others have said, Singh-Ray is reputedly the best. Singh-Ray is, however, very expensive. You need to decide if the price is worth it based on your needs and your shooting habits. I decided that I don't need to pay Singh-Ray prices for my kind of shooting and decided to use gaduated ND's made by HiTech. Not every vendor carries them but I've had good luck at B&H and The Filter Connection (www.2filter.com).