Route 4 to 63 through Litchfield/Goshen/Cornwall/Sharon hands down. Lots of good twisties and beautiful views. Grab lunch at one of the restaurants on the Litchfield green, then head back up. Or stop by Mohawk state park where you can drive to the top and get some more awesome views.
My favorite part is going up Sharon mountain. It's like a smooth togue road--just go slow towards the bottom, there is a hiking trail and people sometimes hike along the shoulder (and sometimes a cop hangs out at that citgo station at the bottom of the hill)
Cops are rare but they do hang out on occasion. Deer are more of a problem than anything.
My #2 pick is instead of picking up route 4 in Goshen is to instead stay on 63 like you're going to Lime Rock but pick up route 7 north, then hop on 44 east in North Caanon which will take you to Winsted. Then hop on route 8 south, get off in Torrington then hop on route 4 in Torrington which will take you back to that roundabout in Goshen by the fairground where you started.