The shortest route from Denver to Moab is on I-70. I've never been on I-70 east of Grand Junction but I found I-70 to be quite ok across Utah. We did a Moab (Arches and Canyonlands NP's), Capital Reef NP, Bryce Canyon NP, Zion NP, Lake Powell and Sedona trip this past August. There were some steep grades but nothing our 28 Class C pulling a Jeep Cherokee couldn't easily handle. We had one member or our group pulling a 35 ft. wheel and they had no problem either except for having to take a slightly longer route (45 minutes) from Bryce to Zion because of a limited clearance tunnel in Zion. The route from Sedona (interesting town with red rock formations, wineries, restaurants and shopping galore) back to Ill would most likely I-40 to Saint Louis. I-40 around Flagstaff is a disaster as are most Arizona
Roads.