I want to get a ND110 filter but don't know which type to choose. I have a P size filter holder with square filters already, and thought this would be the best one for me as I can use it on any lens as I have adaptor rings for all, but I am now having second thoughts whether a circular one would suit better. Is there any real advantage in either type or is it just personal preference? I know there can be colour bias tendencies with different brands. I am only interested at this stage on which type to buy. Square or round.