It is only slightly hilarious to consider this question as I hear news from a concerned coworker of 113 degree temperatures in our collective forecast.
But the answer is obviously mittens. Mittens all the way.
I have poor circulation that leaves my fingers and toes icy even in warm environments. "How is your hand this cold?" is a common question I have received from past companions. That's just an excuse for me to cling to them even harder.
The advantage of mittens is that all of my cold fingers can powwow and commiserate together under one roof of fleece or Goretex or whatever newfangled material REI has just dreamed up. I remember as a child sitting on chair lifts at ski resorts in North Lake Tahoe smashing my fingers up against those sandy hand warmers and pretending to play the piano to keep them moving rather than freezing.
Sadly, mittens are not compatible with cell phones, but this is a problem I only really endured while attending college in Vermont. Thought, better not to mix cell phone and snow (it melts and gets your phone wet like rain) or ice (better watch where you're walking, or you might fall down and bruise your hip/elbow/other crucial body part).
I have a coworker who has a pair of puffin mittens that I adore. They wouldn't do much for me practically speaking, but a girl can admire from afar.
Mittens keep my fingers safe from the elements while I engage in my newfound wintertime hobby (besides reading like a fiend) of snowshoeing. Both hands clamp around poles that help me stay upright while I trample through snow up to my waist.
In the mild California winters, I don't find much use for mittens. Mostly, I just jam my hands into a down vest and ball them up into a fist, mentally counting down the minutes until I can warm them up inside somewhere.
Fingers are important. They tell people things. They help me do math. They let me type these words.
I've just had my morning cup of coffee. Today it will be over 100 degrees. Yet, my fingers are icy.