I use the LEE filter holder, it is high quality but a bit expensive. I have tried cheap Cokin holders, they are plastic fantastic, but they do their job. More important is the quality of the filters. Do not use Cokin filters! I use Hitec filters for ND grads, and LEE Big Stopper for 10-stops ND. For polarizer I use normal screw-in type, without filter holder. I have the Singh-Ray Colour Combo polarizer, but I don't like what it does to the colours. Go for a normal polarizer.