Hwy 200 to 28 to 93 north is one we've done with our 40' motorhome. It's probably the shortest miles. It's very scenic and follows a river.
Hwy 95 north to Hwy 2 is good as is I-90 to 93 north but these would be longer.
On I-90 you will drive Lookout Pass at 4725' elevation - not a biggie but it 6% for 2 miles then 5% for another mile then a gradual descent for another 10 miles.
Toss a coin.