I can't believe somebody suggested that an automatic transmission is better in the winter. That's the most ridiculous completely false statement I have ever heard on these boards.
A manual transmission is easier to get started without spinning the tires in the snow, because you can use as much clutch as you want (it's not going to ruin it, if it's slippery out the tires will spin if you use too much power, so no damage to the clutch). An automatic has much more severe and uncontrollable first gear throttle tip-in.
Also, once you are moving, you can rely entirely on engine braking in the winter, which is MUCH safer and more gradual than applying the brakes, especially if you manage to go into a corner too fast.
Manual is so far superior to auto in winter that it's not funny.
Automatics will up and downshift while you go around a corner, which in the snow WILL end up whipping the rear end out and maybe even put you in a spin, especially in a rear wheel drive car.