Since you have a few SLC days, you might really consider a half-day to Park City and the Olympic facilities there. It's probably less than an hour away from your lodging, and fun to see the ski-jumpers and bobsledders, ect. Good eats up there too.

As for Bryce, there's a high probability you'll have at least a dusting of snow on the formations, along with certain freezing temps at night. It's still really cool, but it changes the way you can hike around when you have to account for ice on sandstone. Some photos and commentary on this blog, which looks to have been in December: https://www.flashpackingamerica.com/utah-travel/best-winter-hikes-in-bryce-canyon-national-park/

As mentioned above, if you're still considering options and not locked into Bryce, you might want to look into Moab/Arches. Probably not much of a driving difference, but the lower elevation means you're going to have milder temps and more accessible hiking.

Can't go wrong with either one of them, as long as you're aware and prepared.