Drive to Oban from Fort William then down to Loch Lomond. The views are stunning
Oban is lovely, and well worth a visit. If I could modify Tails' advice just a little, I'd recommend heading back to Glasgow & Loch Lomond via Inverary, and not via Crianlarich (which is what the route planner will suggest).
RouteIt means you get to Inverary, which is lovely, and the top of Loch Fyne. And you pass
Loch Fyne Oysters, which is well worth a visit...but most importantly, you get to drive over the 'Rest & be Thankful' between Cairndow and Arrochar which, to my mind, is about the most stunning landscape you'll find anywhere in Scotland.