I’ve skiied, not snowboarded Vail and do not think it’s a good of a beginner mountain, especially for snowboarders. There is a nice smallish learning area at the top of Lionshead/Eagles Nest which is easy to access. The best beginner terrain is Sourdough which is not easy to get to. Vail has a fair amount of catwalks to get from one area to another which suck for snowboarders. I haven’t skied Park City so can’t compare. Beaver Creek, Keystone, Breck and Copper are much more beginner friendly. Copper has naturally divided terrain so most beginners are together without more advanced riders screaming past them. With that being said,of the I-70 resorts I think Beaver Creek is the best for beginners. It has two awesome, large beginner areas (Red Buffalo and McCoy Park) at the top of the mountain with another good beginner area at the bottom of the mountain (Haymeadows/Highlands). I never have any reservations about taking beginners to Beaver Creek.