Rent a car for sure! I lived in Breck for 2 seasons. The thing about Summit county is that there are a ton of options. Sometimes Vail will get snow and Breck nada. A-Basin will be insane and Keystone is ice. The best thing to do is to keep your options open to get the freshies!! I personally would not go there without a car. It's cool to check out some of the other towns around S.C. too.
4wd rental. Like Tommy said, you're options can change. We nixed Copper one day due to high winds and went to Keystone to ski the trees. A-basin is just sic, my favorite for sure.
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