Has anyone used the shuttle service between SeaTac and Burlington, WA? Wondering if they are usually on schedule, comfortable, etc.? Is there more than one service company? Do you need advance reservations, or can one just get ticket at Airport when they arrive?

https://www.shuttleexpress.com

Shuttle Express will be WAY expensive for this trip!!! It is great for right around the Seattle area, but I would not opt for it all the way to Burlington.

Take a look at the Airporter. I have not used them, but have heard good things locally about them. Plus they do this route all the time and so the fares are reasonable. I do not know if reservations are required, but I would definitely book ahead regardless since you are going a ways and you would not want to be stuck.

Thank you for the information on shuttle services. We are now thinking about renting a car. Is there a rental car agency off the SeaTac airport that anyone could recommend?

They're all fine, shop aggressively. You might find it cheaper to rent from a downtown Seattle location due to high airport taxes and fees added to the rental car bill.

What does your itinerary look like, when is this, and for how long?

We are going to spend a couple of days in Seattle (no car needed). Thinking about going up to Burlington area to visit older friend. We have someone who will meet us in Burlington, that is why we were thinking of doing the shuttle. How long will be up to us, we are retired, come & go when we want. Will try to rent from downtown location when we decide on hotel in Seattle. Thanks for help.