I've posted on this topic before. Since my daughter used to live in Buena Vista, and since we used to go to Estes Park almost every year, I'm made the trip with our 34' fifth wheel several times.
Here is my preferred route:
Up to Leadville on US 24, Colorado 91 to Copper Mountain, I-70 east to US 6, to CO 119, to CO 72, US 7/CO 7, to Estes Park.
The section from CO 119 -- US 7 is called the "Peak to Peak Highway." I always enjoy the drive, though I take my time. I have told friends, "There is not a level place or a straight place on this highway, but it's a lot of fun to drive."