Yeah we rent.
Hire would involve a human's services, like hire a painter.... and rent a car.
There are not all that many days in Colorado that you would really need a 4 wheel drive vehicle if you are driving city streets and highways.
I would imagine any car that Avis or the others offer will be equipped with the proper tires..snow tires or M&S. I lived there 20 years and only needed chains 2-3 times and that was in the mountains.
Mostly it's about driving skills, technique and judgement. If you have no experience in this area, learning "on the job" in an icy snowstorm isn't really a great idea The biggest advice I can offer is keep a healthy distance from he other cars and don't be in a hurry.