Warm, waterproof and highly breathable is best. They must be windproof and
if your hands are to stay warm, not too tight. If you're snowboarding then
extra re-inforcement on the fingers is recommended as dragging your hands on
the inside of your turns will soon wear through the outer.
Gloves with built in wristguards are a good idea if you are snowboarding.
If you have separate wristguards and many do, make sure you buy a glove big
enough to accomodate them with reasonable ease.