Probably might be a bit late to reply since the ski season is almost over or already over for some ski areas. Anyway I have skied at Beaver Creek and Snowbird amongst the resorts listed and I consider Whistler as my 'home' mountain since I spent countless weekends there when I studied and worked in Vancouver for a time. Personally I found Hugh's Heaven and Cloud Nine about the same, and while Hugh's Heaven is slightly steeper, it is more consistent on the way down, while Cloud Nine can get bumpy at times and it does have some steep sections and if not careful could lead to a moguls section. In general, the blue runs at Whistler side is milder than the ones in Blackcomb side.

Amongst the resorts you listed, Beaver Creek is generally easier for the equivalent blue runs and generally better groomed. Also the ski resort is more suitable for families. Snowbird is more of a local mountain with most skiers coming up for the day, and I found its terrain to be a bit more narrow and steep even compared to Whistler. I did, however, enjoy Mineral Basin in Snowbird but it is more like an open bowl which is my preferred terrain in skiing.

Speaking from experience, I would not suggest relying solely on a piste map colours to gauge difficulty as under some conditions, a Black run can be easier than a Blue run. I was at Snowmass and upon a recommendation was told to check out 'Campground' which is a Black run but I enjoyed that run the most during my visit since it was empty and the piste was not as steep as I thought it would be. So checking out the terrain with a guide or just asking for recommendations from the guest services would be a great idea at the start of your ski trip.