I couldn't give you the exact number, but as is typical with these Cascade passes, the climb from the east is more gradual than the drop on the west side. I believe heightwise US12 is lower than US2 (Stevens) but higher than I90. I've only driven it in a car, but it doesn't have a bad reputation.
And what's your alternative? I82 to I90 has a pass, not high, but generally high speed, followed by I90, and a long drive down to the Rainier area. And in the Rainier area, White Pass is the easiest - except for continuing west down the valley of I5. You'll do a lot more climbing in the tow/toad to see the Rainier sights.