Canyons Park is pretty Epic but generally CO is going to win for Parks
No questions CO easily takes the cake for nightlife
I live in the Cottonwood Heights\Sandy\Midvale area which is 10 minutes from downtown SLC and 25 minutes from Brighton, Solitude, Snowbird and Alta. 40 Minutes from Park City, Canyons and Deer Valley and 55 Minutes from Powder Mountain and Snowbasin all world class resorts with EPIC terrain and some of the best backcountry access in the world.
Night life in park City is pretty good but not quite up to CO levels
My advice is to wait and see how the snow develops in mid January and then go from there, been a crazy weird weather pattern year here. IF was Summit County CO today versus SLC I would easily take SLC but who knows how things are going to change in the next month so follow the snow predictions.