The San Jauns can't be crowded in summer - because all you Yanks are in our Gulf Islands and Desolation Sound!
Seriously, though, both areas have their pluses. The biggest knock on the San Juans and the southern Gulf Islands is the cool water temps year round. Another major factor that can catch newbies unawares are the tremendously strong currents in the northern San Juans and southern Gulf Islands in the border areas.
As you head north beyond the Gulf Islands, water warms up and swimming is more enjoyable. Should you get to Desolation Sound there are the additional pluses of several fresh water lakes withing easy hiking distances of some very nice anchorages.
In between are must-sees like Jedidiah Island, Jervis Inlet and Princess Louisa Inlet, not to mention Tribune Bay on Hornby (weather dependant).
In 25+ years we've always found a spot for the night - and discovered some neat one-boat nooks along the way.