While I understand that Kansas just seems to go on and on and on, my husband and I have used I-70 anyway. The portions beyond Denver in Colorado, and all the way through Utah, make eastern CO and the flat end of KS just something to tolerate. (We like the eastern end of KS, with the rolling hills.) Hubby and I prefer I-70 to I-80, for the reasons of scenery.
US-50 would be an alternative, just remember in NV it's called "The Loneliest Road" for good reason. Be sure to fill your gas tank and keep it up!
Donna