I worked down there for a number of years. I had a work Visa and would be down there usually every week and the Visa allowed me to live in Canada.
There are some nice neighbourhoods in Seattle proper and like our Downtown Eastside, some not so nice places too.
My work typically took me to Redmond which is where Microsoft and other high tech companies are located. It is pretty upscale and it is located across the lake on the East Side of Lake Union. Nice neighbourhoods and shopping etc. Further north from Redmond are some nice areas too but you would probably be commuting which is incredibly bad on the Hwy 405 in the AM.
If it were me, I would choose the Redmond area because I spent so much time there, felt safe, easy to get around, had plenty of outdoor activities, good shopping and it still had a country feel to it being so close to Seattle. Bellevue is located to the south and west of Redmond it is pretty much the same atmosphere.
Mercer Island is a nice place too and it has some of the pretty expensive real estate. I only drove around it to take a look.
It really depends how much of commute you can tolerate when you live in the Seattle area. They do have an effective grid of highways compared to the Vancouver area.
Best restaurants are located in downtown Seattle IMO.
They are attempting to clean up the areas near Qwest Field etc but at night time it becomes crack central. Avoid it if I were you. Still they have made an effort to replicate our Yaletown neighbourhood with old buildings being gutted and keeping the exteriors.
The University (U of W) district is a nice neighbourhood too and it is really quite close to the downtown.
To the south is Renton, Tukwila, Southgate etc. Pretty much suburbia.