OP, I think you may need to factor how long your stay is, what would be must-do's, what your interest is, size and makeup of your party and are you renting a car. If you want to see the city, Everett is a bit far, not crazy, but 40 minutes is typical from there to downtown Seattle. You have Rainier National Park to the south, Hoh Rainforest in the Olympics on the Peninsula to the west, with ferry options for your vehicle, and are at the foot of the Cascades (Snoqualmie Pass) to the east, with small mountain towns and lodging options if you want to stay away from the density. If you don't want to rent a car, but still want to check out the City, Ballard has light rail options to downtown, SeaTac airport and both the UDistrict (their Dinkytown) and a stop right at the stadium. The Mariners have a weekend series vs the Angels and Tix are similar in price to the Twins, and it is a nice ballpark. If you are mobile, definitely check out the natural scenery. As others suggest, San Juan Islands, Bellingham and Vancouver (passport needed) are all great options up north. Also a full day option is Leavenworth, a Bavarian-themed town with a big pavilion/plaza area in the heart of town, surrounded by great hiking options. Also, check out McMenamins, it is a PNW-only company that rehabs old properties and turns them into unique hotels with bars, restaurants and events. There is one in Bothell that is pretty cool called the Anderson School. Since the Gophers are now coming to this region, you can have fun checking them all out, some are in really nice locations.
I have only lived over here for 5 years (Everett, now Tacoma), so I am not going to have the best knowledge, but I will offer opinions where I can.