The ES SEA is on the West Valley Highway near Southcenter Mall, so you would have to have the hotel shuttle drop you off and pick you up at the Tukwilla station. The DT SEA is showing rates of ~$70 some of the weekends coming up and you could just walk down the street and catch the train at the airport.

The Hampton downtown has rates for some weekends coming up of about $110 but you are about a mile from the convention center and other areas of downtown. The Homewood Suites Pike Street Seattle Conv, Center will be cheaper than the Hilton and may be just as convenient. It's a nice property. The Sheraton is just a couple of blocks down the street.