this information has to be placed in context: about 80%¨of all heat gets lost through your head when the rest of your body is properly insulated.
because let's face it when we go skiing the only part of our body that is exposed is our face/head. same goes for sleeping bags, here its sometimes even around 95%of all heat that gets lost through the head!
But when you would by example get lost in your Tshirt in a snowstorm, don't start looking for a hat first, most heat will get lost through your torso, so look for a proper jacket first...
But in this case, let's asume we're in proper winter outfit, except we're lacking gloves and a hat, the logic answer would be a hat, your ears will freeze off sooner then your fingers+ you can allways put your hands in your pants or armpits....