If you're planning on staying near the stadiums or in the general city centre, just take the LRT from the airport. There are stations that go through the city centre and to the stadium.
You might not even need to rent a car. Taxis are plentiful and Uber is all over the place there. I was just in Seattle about 2 weeks ago and none of my Uber rides (except for 2 trips out to Bellvue and back) were over $8.00. All told I spent about $120 over 3 days on Uber. No rental car charges, no parking and the ability to drink/smoke without having to worry about driving.
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