Not wishing to contradict any of the above but factoring in the amount of parking and the uniqueness and beauty of each place, you might want to consider trying a couple of these, especially on your first visit to the area. The very early starts are essential for the most popular hills with relatively limited parking, for many other places and even the hotspots, 9am or 10am, or after 6pm, is unlikely to be busy enough to spoil the experience.
If you don't fancy climbing the taller hills, the Nevis gondola rewards you with excellent views on a good day, with minimal effort and plenty of parking. It is pricy though, and can be busy. Plus it's a tiny detour on the way somewhere if the car park is too full, and has forest trails and mountain bike hire.
Arisaig and Morar beaches will certainly be busy by midday but there is a fair amount of parking; maybe a bit limited with a motorhome, much easier if you have a runabout in tow. They are stunning on a sunny day and there is nothing else like them on the mainland. Don't miss them for fear of crowds! At their worst they'd be about 5% as busy as Brighton.
Similarly there is quite a lot of parking in Glencoe with people coming and going all the time, and it offers amazing views from Buachaille Etive Beag and Pap of Glencoe. They'll be busy by Scottish hill walking standards - but for me that means seeing more than two other people on a four hour walk
Depending on your travel plans, I'd try to fit in a stop at Luss on Loch Lomond if you'll pass it early or late. It gets insanely busy, but it's beautiful and it'll be your first taste of what the Highlands have to offer, even more so if you fancy hiring kayaks there.