I like the rebuilding of PDX's concourses in the earlier part of the last decade. The main terminal is still somewhat outdated, even though they have built a nice "umbrella" over the entrance areas, and has a nice shopping area just beyond the ticket counters.
Seattle built a new central terminal about five years ago, and it still stands up as just beautiful. The central terminal offers many food choices and a great picture window of flight activity.
So, right now a tie. Seattle is great in the central sections, but PDX concourses are bigger and easier to navigate.
For you frequent flyers, compare the airports.