Actually you've got multiple choices. Every access is brilliant. The Umbrail Pass (Switzerland) is partly dirt road, but well maintained. Of course the pass is closed during the winter season, but to my knowledge all three access roads are open in summer.
I'd suggest to ride from the east (48 hairpins), pay a short visit to Sitzerland via the Umbrail Pass, return and carry on westwards.
Only when we pause to wonder
do we go beyond the limits of our little lives.