No opinion on the Hoya from personal experience. In fact, none on the B+W, either, since I bought my 82mm 10-stop before B+W released theirs, and the only 82mm screw-in 10-stopper was from Schneider Optics. They're the parent company of B+W, but I don't know if the glass is the same. I have the 77mm B+W 10-stop, the color of the two is similar.
My Schiender does add some warmth to the tone, easy enough to WB out in post. I've read that the Hoya is off to the cool side.
I do think the extra stop would be worth the slight additional cost, though. If you're at ISO 50 and need that stop, you have it. If you don't need the stop, ISO 100 or 200 won't add any significant noise to the shot. Also, you may want to stack a CPL onto the ND, in which case the brass rings of the B+W mounts may mean less likelihood of the filters getting stuck (but have a set of wrenches, just in case).
Below are a pair of shots from a couple of weeks ago, the first with the B+W 10 stop (77mm) on a 24-105mm, and the second with the Schneider 10-stop ND (82mm) on a TS-E 24mm II. The first is f/9 and 15 s exposure. I was at ISO 400, and could easily have used 30 s or a bulb exposure by dropping the ISO - but, the scene was shaded. The second shot was at f/7.1, ISO 50, and that gave a 4 s exposure. Getting down to a 30 s exposure would have put me well into diffraction territory at f/20 - that's a case where the extra stop of a 10-stop vs. a 9-stop filter is good to have.
Have a good trip!
