score:3
You basically have two choices, I-90 and I-80 to I-84. I-90 is more direct, but only by a few hours.
Both routes are as safe as any interstate highway except during snow storms and shortly thereafter. I would plan to take I-90 unless there were a snowstorm that somehow affected I-90 without affecting I-80 or I-84. If there were a snowstorm affecting both, it would probably be best just to wait it out.
In other words, use the weather forecast to decide which route to take.