Two questions come to mind - where do you want to sail and how long will your charter last? If you plan to sail the US San Juans only, Bellingham is a good choice. If you plan to sail the Canadian Gulf Islands or Desolation Sound - this would be my choice - I agree with Richard Elliot. No personal experience but I've encountered Desolation Sound Yacht Charterers who were pleased with their experience.
For the San Juan Islands, I recommend San Juan Sailing. Six years ago, I chartered with San Juan Sailing in Bellingham and was very satisfied. Over the past 2 years, I've had 2 different groups of sailing friends who chartered with SJS based on my recommendations and they all had a good time. For the past 5 years I've kept my own boat at the US/CN boarder in Blaine WA, but spent 90% of my cruising time in Canada.
If you only have one week, I would not recommend trying to sample both the San Juans and the Gulf Islands - it's too rushed.
Jeanneau 37 - Windfall