How active or adventurous do you want to be?
My parents and I had a fab trip last year - renting a minivan and driving up part of the west coast, over through the Highlands, down the East Coast, over to Skye and into Glasgow.
There's a gorgeous B&B/family home just outside of Glasgow where we stayed with the loveliest family (and cutest dog EVER)... in the most beautiful, pristine surroundings (there's a stream that goes right by their front door), you'd never know a big city was nearby... and right next to the last of the Highland distilleries (Glengoyne).
Overall I'd say anything that involves the Highlands.