I always take the Cascades (from Tacoma), but that's just a schedule thing. For the short trip it doesn't make that much difference, and I learned two days ago that the Coast Starlight now has a business class car with the same amenities as on the Cascades (well, I'm not sure about the 2+1 seating, but you get the free water, wi-fi, $6 food credit, etc.). My next trip is through to Emeryville so no-brainer on that one.

The only other consideration could come into play if someone has trouble walking. Unless you're on one of the Cascades trains that goes through to Eugene, they tend to stop in the Portland station short of the pedestrian crossing over the inside track. This leads to a considerably longer walk from the end of the train -- or even the head of the train -- into the station building.