I-70 through the Rockies is indeed very scenic (Glenwood Canyon is worth the trip IMO)... it also has a LOT of long, steep grades, including two passes over 10,000 feet (Vail Pass and the Eisenhower Tunnel). Not the easiest route to tow a camper.
If you want to do the northern route I would consider taking highway 13/789 north out of Rifle into Wyoming, a much easier tow route, and still pretty scenic if not as spectacular.
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