IMO I would base myself on Orcas. It is the biggest and has the best riding with Mt Constitution as the center piece. It has a nice state campground, good places to eat and quite a few lodging options. There are ferries that go only between Orcas, San Juan, Shaw and Lopez. Getting on the ferrries can be a hssle with long line in a car, especially from San Juan but are easy on bikes. Locals park in line and go eat meals while waiting on weekends. Shaw and Lopez are flat and are supposedly pretty easy loops although I've never ridden them.. San Juan is ok IMO but it has quite a bit more traffic and any area around Friday Harbor is not the greatest riding. The opposite side where the English and American Camps parks are at are is a nice out and back ride if you drive out of town a little.