US2 is fine all the way to Glacier, but out of the way if headed to Yellowstone.
It's a good option across the Cascades if coming from the north. It saves you the city freeways from Everett to Issaquah; but the suburbs have crept out to Monroe and Sultan. And it's pass is higher and steeper than I90's.
East of the Columbia it's a toss up as to which is better. Last trip to Spokane and back, I flipped between the two in both directions.
Coming from Vancouver, I'd consider taking WA20 across the Cascades; that comes first and is even more scenic. But all the Cascades crossings are scenic, even I90.
