I would agree both resorts would typically be in full swing barring a strange year. The Boat typically gets a little more snow than the Summit County resorts, however, it would be a negligible difference in most years.
I would argue Copper has better intermediate terrain only because it seems laid out in an easier manner to locate.
The intermediate terrain to the base at Steamboat might involve a long catwalk.
In addition, if for some reason Copper lacked snow Loveland or A-Basin would be close and would likely have better coverage. Loveland has superb intermediate terrain.