PDX's MAX light rail station is about 150 feet from one of the AS carousels; about the easiest public transit system in the USA for a traveler to access. On the other hand, the light rail station that serves SEA is probably 1/4 mile from the terminal and requires walking through a parking structure.
I think my favorite transit system in North America is Vancouver, BC, which features the driverless SkyTrain. If you have the time you can take public transit to Victoria via the wonderful BC Ferries and connecting buses at Tsawwassen and Swartz Bay or as far east as Chilliwack and nearby Harrison Hot Springs by bus.
I loved the MTR system in Hong Kong and still have my Octopus Card.
Tokyo has probably the most extensive rapid transit rail system, even over London, Paris and New York.
I am always amazed at the public transit networks in German speaking cities such as Munich, Frankfurt and Vienna. I was in Basel earlier this week and loved the trams there; Bern has both trams and electric buses (overhead catenary, like San Francisco and Seattle) which seemingly go everywhere in the Bern region. Budapest is another place with a great tram network and a number of subway lines.