For SEA, you can take the light rail to downtown, where there are several nice Hyatt properties within a couple blocks of a station. Once I looked at the newish Lake Washington HR property, but people here convinced me that this would be a bad idea for use as a substitute for an airport hotel in that the drive tends to have bad traffic, there's no airport shuttle, and there's no reasonable public transportation either.

BTW, at one point when I checked, I learned that SEA airport hotels tend to charge a fee to use their airport shuttles. IIRC for the full service Marriott very close to the airport (maybe even walkable if you don't have much luggage, but it seems to be across a big street and then uphill) the fee was $6 per person.