Summer getaway to the Rockies
If you are looking for a cooler climate, Colorado would be the better choice. In Utah, most areas like Park City are still hot during the day. For Colorado,it would depend on the type and level of activity you want, from a quiet area like Winter Park to a more active area like Vail. Vail typically has some fun outdoor concerts(free) that we always enjoy.
River rafting in July will be milder as the snow runoff has slowed considerably, but the head waters of the Arkansas River is just a couple of hours from Vail and would be a fun trip for you and the kids (if any).
The Durango area in SW Colorado presents another diversified choice for the ATV/biking enthusiast. There is a fun scenic narrow gauge railway to Silverton.
IMHO, Steamboat Springs is more of the touristy type choice.
The Rockies are a popular summer destination, so you want to reserve soon.
Ron Reid