What are you trying to ski? Park, big mountain, both? Winter Park and Eldora will be shorter drives, so Ikon is good on that if you don't want to mess as much with I-70. Neither one of those has great parks, so you'd have to go to Copper for that. Epic is pretty much all Summit/Eagle, so you'd have to deal with the drive all the time but get better parks and bigger mountains with more crowds. Epic will get you skiing earlier with A basin if you don't mind hiking rails or skiing the white ribbon of death in October (depending on weather obviously). I don't know much about Crested Butte or Steamboat, Aspen is definitely worth skiing but that's going to be a bit far for a day trip from Ft Collins.
If you're planning on going to Utah at some point, the Ikon resorts are way sicker than just Park City.