Definitely drive I-70, not I-80.
Stop at all of the view points along I-70. You can get a mini glimpse of the San Rafael Swell.
How long do you have to sightsee? There are a million places to go.
You could take I-70 to past Dillon and turn north at Silverthorne on CO-9 (Colorado state route 9) to Steamboat Springs. That would be a reasonable stop in the mountains if you want a one night / two day drive.
There are several alternative longer routes if you want to take longer. (a) Go through Estes Park and Rocky Mountain N.P. or (b) Aspen to Leadville to Gunnison, or (c) aim for Durango and Mesa Verde N.P.
You could even go north through Yellowstone and Grand Teton N.P. if you have at least four or five days.
What are your constraints?