Well, as a veteran of both the Slog and the drive from Bakersfield to Sacramento (or for a three hour equivalent, Fresno to Sac, which I will call the Fog) I would vote for the latter as much, much longer. The drive from Portland to Seattle has turns. It has trees to view. It has rest areas. It has paved roadway. It rarely has fog. It's no contest.
Being a Texan and not knowing much about the Great Northwest we got on the Slog out of ignorance .Last year after The Oregon Gathering we were looking for a direct route to our sons home in LaConner Wa . OOOPS!!! Why didn`t some one tell me?
Well, not doing it as a commuter, I schedule the time I hit the road carefully. At the right time of day it is 3 hrs from Portland to the Mukilteo ferry north of Seattle. The trick is timing it to avoid traffic in Portland, Vancouver, Olympia, Tacoma, and Seattle, and there aren't many ways to do that. Wednesday morning I'll probably leave Whidbey about 9 and go through Seattle about 10, Portland 1-2, and that works pretty well. Obviously would not work for a commuter, though.