I've sold my cokin polarizer, although the cokin system was very useful for my Mamiya film days, with digital I found the polarizer caused me problems with very fine detail using FF hi res DSLR's.
I want to invest in a good quality polarizer, multi coated and slim so I can use it with WA lenses should I choose to.
The choices are the Hoya Super Pro 1 polarizer or the B+W Kaesemann MRC polarizer. Both are 5mm, both multi coated (the hoya has more layers) and significantly, both use aluminium rings (this is the only B+W that does!). The Hoya has a front thread for stacking but with digital the need to stack is very small. The price is similar to equal.
Anyone have any opinions?