North to south, Utah’s I–15 spine is longer than the drive from New York to Montreal, so Utah’s pristine beauty requires motorized transportation (car, motorcycle, or RV) for access. In summer, winding mountain roads and long dry basins are either a boon (convertibles, motorcycles) or bane (some roads were clearly not built with RVs in mind). In winter, high elevations and serious storms make a sturdy car the best option. Storms occasionally shut down highway passes and/or resort access, so be flexible.
About the only places you can do without a car are Salt Lake City and Park City. You can enjoy three world-class ski resorts in Park City without a car (grab a taxi or shuttle from the airport and ride the town’s public transportation), but it’s harder to get to resorts like Alta, Snowbasin, or Snowbird without a car.