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My answer to your question would be none of the above. That's the real danger of computer programs, where if you turn your brain off and only look at the options a computer spits out, you could end up in some big problems.

Both of those routes are almost all 2 lane roads, through some of the most remote places on the continent. If there is winter weather, you could find yourself in a bad situation with really no where to go.

The route I'd recommend is very simple: I-84 to I-15. It's all freeway, all heavily traveled, plenty of services, and roads that get top priority if there is winter weather. It adds about 100 miles to the trip, but it is on higher speed roads so travel time isn't likely going to be much different. No matter which way you go, you'll need an overnight stop anyway - that's far more important to your safety than route choice - and sticking to the Interstates will give you many more options.