If you'll be in Oban at all, I can recommend the Oban Perle - it's less than a year old. We just stayed for my father's 60th, and it is by far the nicest full service accommodation in Oban. Both of our rooms had wonderful views of the harbor, Beds were comfy, bathrooms large (and Aveda products), and they sent up local chocolates and champagne for my father's birthday.

I echo that you won't find many chain properties in Scotland. There are several around the airport (Marriott, Moxy which is within walking distance). We have stayed at both the Shertaon Grand and Glasshouse Autograph, and found them to be fine.