If you're not used to driving in the snow, I wouldn't recommend hiring a car. I did a trip in January, where our group of friends were pushing me to hire a car. After speaking to someone who has done many trips to the alps, he advised to rather get a bus.
I must say his advice paid off, had a relaxing trip to the resort, La Plagne, when we arrived there our friends looked stressed and said they would never drive on those roads again. Unfortunately for them they had to drive back a week later.
Cost wise, for two of us our transfers were approximately the same price as car hire, with 4 people the car hire would be cheaper, but also take into account how much baggage and gear(boards etc if you have) the vehicle can carry.