I'll add another vote to the Link light rail. It's the backbone of seattle transit and will get you to Sea-Tac in around ~45 minutes from Westlake.
I'll also put in a good word for the buses, though they're lacking from what they used to be. If you don't want to take the Monorail to Westlake or another Link stop, Google Maps should help you out with the bus routes (it's quite accurate on the routes, though its usually off by a couple minutes on the stop times).
The monorail is great if you need to go to:
- Seattle Center (where McCaw Hall is at)
- Westlake Center
But it makes no stops along the way, so good luck if you wanted to go anywhere else along the line. Also last time I rode it, it only took cash(!?).