Warmest ski gloves and mittens
There are a few factors that determine whether a glove or mitten is warm. The amount of insulation, the materials used to make them, moisture management, your circulation and the type of activity you intend to use them for.
If you have good blood circulation and your hands rarely get cold look for a pair with minimum insulation, maximum breathability and good moisture management. This type of glove will keep your hands warm by effectively moving perspiration from the inside of the glove away from your hands, especially if you are skinning up hill, skiing moguls or hiking. Leather gloves usually work best.
If you have poor circulation and or ski very fast look for a glove or mitten with heavier insulation. As a coach, I usually spend the whole day on the hill skiing fast! Depending on the weather, if is 20F or above I will usually go with a nice insulated leather glove. If its below 20F I'll go with a heavily insulated leather mitten. On really brutally cold days, I use heater packs.