I've skied 4 times at Winter Park but only visited Steamboat during late summer. Skiing wise I think they would be similar - I've heard Steamboat gets more powder and would probably track out slower, but Winter Park definitely has good beginner and intermediate terrain for the kids. Winter Park is my #1 suggestion for easier skiing in CO. Other things to consider:

Winter Park is about 1 hour from Denver, Steamboat would be ~2.5
Winter Park has a village, but no real town around it, Steamboat has a nice little mountain town with shops
Steamboat has Strawberry Hot Springs (must do), Winter Park has hot tubs in hotels
Winter Park is closer to other resorts/towns like Breckenridge/Dillon/Frisco, Steamboat is fairly isolated
Both have good skiing
Both have good scenery
Both would be a good ski destination