There is a bit more truck traffic on I80 through Nebraska than 70 in Kansas. Both roads are in good condition and there are plenty of places to stop along the way. I'd suggest I80.
Having lived in Denver for many years and traveled back and forth over 25 times between Utah and Michigan, I would take I-80 in a heartbeat....A little more truck traffic but generally an okay ride across the mid-west.....JMHO