It's been a couple years since I did it, but it's a pretty taxing drive. I think it's close to 3 hrs, depending on weather, of course. There are shuttles which are comfortable and go frequently, but I thought they were pretty expensive. I want to say something like $55....maybe it was $35 each way. I just remember thinking it was steep.

Depending on where you're staying, having a car can be a pain in Vail. Parking is not easy or cheap, so if you're staying close in the Village I would recommend the shuttle and living without the rental car.