+1 for the Dukes Pass down to Aberfoyle – hairpins, great scenary and a good road surface. In the wet it can be a bit testing getting round those hairpins though!
I prefer the ascent/descent from the Rest and be Thankful along the B828 (Hells Glen) rather than the main road.
Some other favourites:
The String Road in Arran is great on a nice day looking down over the water – the top section in particular is fast – only hill in the UK where i’ve managed to hit 60 mph. Lochranza to Glen Sannox would be good too if it wasn’t for the awful road surface
The C11 road from Glendaruel to Otter Ferry – bastard of a climb to get to the top but nice descent with spectacular scenary coming out the treeline and overlooking Loch Fyne and then the pub at the bottom on the water.