I enjoy seeing the mass transit in different locations I visit and will take the train/metro/subway whenever possible as I usually pack very light and have no troubles navigating the stations. I have quite the collection of contactless transit payment cards, hopefully contactless credit cards will become more accepted.

As OP mentioned the light rail at PDX is cheap and convenient. I also like the train to/from SEA as it can be faster than driving when traffic is heavy thought the hike across the parking structure is longer than I'd like.

Stockholm gets my vote for most impressive stations, Berlin for efficiency and connectivity to inter-city rail.