So I'm looking at getting some graduated ND filters (and possibly some others), but I'm a little confused at all the different options and need some help choosing which ones are right for me. From what I can see there are two main brands, Cokin and Lee, with the latter being quite a bit more expensive. Is there really that much difference between the two or should I just go with the cheaper option? Also, I assume I can just buy any filter holder and use any other brand of filters with it (assuming they are the correct size of course). That brings me to my last question - what size should I buy? Cokin seem to do a range of sizes (A, P, X, Z series), but I'm not sure which would be most suitable for the lens I will be using - mostly a Nikon 12-24mm with a 77mm filter thread.