The van is now approaching that 200,000 mile[stone]. Interstates are always best as far as speed limits, amenities (i.e. 24 hour rest areas, truck stops, etc.), lighting, smooth pavement and everything else that makes living on the road for months at a time more comfortable. But in most cases interstates are not the shortest route to your destination.
Those who have traveled a lot between the Midwest and Southwest (for me, Des Moines to Phoenix) have probably used the I-80 to I-25 in Denver route until you get to I-40. The scenery in Colorado, along with the atmosphere, is always worth the trip. But that route extends 1,600 miles. I decided to try the Kansas route that is only 1,410 and takes two less hours than the interstate/Colorado route. You also still avoid Texas entirely (albeit by only about 2.5 miles).