Quick Shuttle is slightly more "upscale", to the extent that term has any meaning in respect to bus transportation . Quick Shuttle is nice because it goes straight from SeaTac (or straight from downtown Seattle) to Vancouver airport and various points downtown. In my experience, Quick Shuttle was cooperative about letting me off where I (or other passengers) wanted to be let off. Greyhound is rigid - it makes several stops in Washington state, a stop in New Westminster, and a final stop at the Vancouver bus station (near Main and Terminal).
The disadvantage of both Greyhound and Quick Shuttle is that they run only a few times per day.

I haven't taken the Grayline shuttle from downtown Seattle, but I've heard it's a good service and is good for transporting luggage. However, if you get Quick Shuttle from SeaTac, you obviously don't have to switch. Edit: Last I heard, Grayline shuttle to the airport from downtown Seattle was $8.50.

Greyhound is definitely cheaper than Quick Shuttle, at least without special deals.


[This message has been edited by WillTravel (edited 06-17-2003).]