I've used the Hoya HD (I have a 72mm CPL) and now use the B+W (77mm CPL) - they both appear to be well made and nice to use (the B+W heavier and as Peter said appear to be better built).
NB: I purchased mine online @ maxsaver.net and the price difference between say the 77mm Hoya HD and the B+W F-PRO MRC (or even KSM which is on special
ATM) is perhaps not as much as you might expect.
The Hoya HD is slimmer though (and has front thread) so that may matter if you're using on a really wide lens (vignetting) - there is a slim version of the B+W but I don't like how it doesn't have front threads and has a pop on cap but thats just me. If you're shooting really wide you may not want to use a CPL anyway since you get variable polarising effects across the frame (because of the extreme angles of view).