No offense but here is my reasoning for recommending avoiding those. If you are sitting in the passenger's seat and enjoying the scenery they are great drives and very doable. I drive both. The 87-260 route more than the other but I am driving and it is really difficult to look around and enjoy the scenery, especially on the 2 lane mountain sections, at 65, with 3 tons of trailer behind you. There is no white-knuckle issue it is just paying attention to the driving. So I generally try to recommend the routes that will give the trailer hauler a route that will have more lanes and less side traffic to deal with.
His best route is I-17 even with the long climbs but for some reason he did not want that one.