I prefer US-50. I'm not in a hurry. I usually pick it up somewhere between Hutchinson and Dodge City, so I can't speak for the eastern part, though I expect it to be as good as US-36, US-54, US-400, US-160, US-166, all of which I've used to traverse Kansas. Kansas takes good care of the roads at this level.
If you take 50, be sure to make a stop at the Bent's Fort reconstruction. This is a National Historic Site on the Santa Fe Trail, about where it stopped going west and turned south toward Mexico. Take in Royal Gorge, also, if you've not yet seen it. The Arkansas River canyon is impressive, but what is most interesting about the site is that this is one of the first places in the west where the local businessmen recognized that a natural feature had value as a tourist attraction and invested an enormous amount of money to make it so.
I'm usually not in a hurry, when I am I'll use the Interstates, but here in the middle of the country, the Interstates don't go everywhere. It is almost as if they don't go anywhere, except to connect a few really large cities with professional football teams, and bypass anyplace interesting.