If your time is fairly limited, I would recommend Whidbey over Orcas. Although Orcas is lovely, the hassle of getting there (especially in summer, and especially when starting from Pt. Townsend) could be a real disadvantage.

Easiest way to get from Pt. Townsend to Orcas would be by plane. There's a small airport in Pt. T., but I don't know if regular flights go from there to the San Juans.

I really think your best bet is Whidbey - it has several nice small towns with galleries, B&Bs, restaurants, shops, and, if you crave beaches, it has some lovely ones.

Have a good trip!

Julie in Seattle