I've only ever crossed at Blaine once and the traffic south through SeaTac was horrendous. 101 to Olympia Mon-Fri looks like it would be a great option, seeing as your starting point is PA.
Mike. Comments are anecdotal or personal opinions, and worth what you paid for them.
2018 (2017 Sprinter Cab Chassis) Navion24V + 2016 Wrangler JKU (sold @ ????)
2016 Sunstar 26HE, V10, 3V, 6 Speed (sold @ 4600 miles)
2002 Roadtrek C190P (sold @ 315,000kms)