Best gloves/mittens for winter?

Are you asking for single digit temps in F or C? What is your expected activity level?
The difference between what chair lift operator at a ski resort and a skate skier uses would demonstrate the difference.
Even with a modular glove system the operator still is inclined to use disposable handwarmer packs where as a skate skier can use toko split finger mittens [lobster style] or something like mountain hardware's epic glove.
The next question would be what level of waterproofing are you looking for, single digits usually preclude the need for much else then a nylon shell, brushing away accumulated snow keeping body heat from causing a melting effect, but most glove systems come with some form of waterproofing/water resistance anyway.
The next question is what level of grip and dexterity do you need? This alone might determine whether you are looking at a glove or a mitten.
The high end mittens have a shell with at least synthetic insulation[mostly primaloft] on the backs and usually a removable fleece liner that can be dried with body heat in your bag at night. Outdoor Research Alti, Mountain Hardware Absolute Zero Mitts, RAB Exped mitts, and BlackDiamond Renegade [wool liner] are at one end of the range.
Not knowing the answers to your needs my two favorite gloves are the Black Diamond Guide [fingered with wool liner] or the Outdoor Research Zenith [mitten but with fingered insert] both allow dexterity in cold weather.
If you are ice climbing look for a sticky glove and if you can find a mitten with a nose wipe surface that's a plus.
Experience plays a huge role in glove selection, for just backcountry skiing I use either Marmot Work or Ibex Climawool or Backcountry Gloves. I also carry a pair of spare thin liners in a fanny pack.
Since it's plastered all over the home page maybe somebody could tell you a thing or two about Bozeman's Featherlite Mitts.
It's 21f and I forgot to bring any gloves to work today so what do I know.