Let me offer my opinion...
I was also on the quest for the best pair of mitts this year. I tend to go overboard, so as a result, I ordered 8 different pairs of mitts from the following manufacturers (yes, I know I have issues). I ordered each manufacturer's top of the line mitt.
Now, I haven't used any of the mitts on the slopes, but I've tried them all on several times at home. The Black Diamond Mercury Mitt is definitely my favorite and it's the one I kept coming back to. Many of the mitts have a flaw where the inner lining doesn't flex at the same point that the outer shell does, making it tough to grip things like ski poles. This was a big issue on many of the mitts I tried.
If it weren't for the Black Diamond Mercury Mitt, I probably would have chosen the Hestra Gore-Tex XCR mitt (see hestrausa.com). Neither were perfect, but I felt that the Black Diamonds were better overall. My only real complaint about the Black Diamonds are that they don't use gore-tex, but instead use a proprietary membrane called Bdry. I'm sure it's fine, but would have preferred gore-tex as it's most likely more breathable.
The Hestras biggest flaws were:
1. The leather is white and there are no other options, so they'll probably get dirty and look bad pretty quickly.
2. The inner liner is not removable (not as big of an issue for some, but it's a nice feature).
3. The insulation is fiberfil/qualofil and not Primaloft (far superior). Most of the gloves I tested (if not all) had Primaloft except for the Hestras.
Other than these flaws, the Hestras are well designed and seem very rugged. I just think the Black Diamonds are better overall. You can get them from REI or Backcountry.com - both of which have unconditional money back guarantees even after using the product if you're not 100% satisfied. As a plus, the Black Diamonds are cheaper than any other mitt I tested ($80).
And yes, all the other mitts have been returned!