I’m from Scotland and it totally depends if you want city or countryside. If city then definitely Edinburgh. If countryside/seaside then Oban is beautiful. So is the Isle of Arran. And Perthshire around Aberfeldy is gorgeous too. I would recommend visiting at least one of the lochs too like Loch Ness or Loch Tay.
Glasgow. Fabulous city - great parks, museums, theatres, shopping. You can be at Loch Lomond in 30 mins for walks, breathtaking scenery. Alternatively, Inverness. It's much smaller but it's cute plus you have Loch Ness and Culloden, etc.
Thanks all! We'll land in Edinburgh so thinking couple of days there. Then highlands and stay in cairngorms for thrill stuff for teen. Then week around Oban/western highlands, maybe night in Glasgow then back to Edinburgh for flight home.