This is a tough choice… I saw another entry you wrote mentioning Sonoma County too… Both valleys have amazing wines, however they are two different experiences. The Napa Valley consists of one valley and the wineries are concentrated and is easier to navigate. Sonoma County wineries are spread out and is divided into many different appellations and regions, and geographically are different. It would be very difficult to choose “one”. That would be difficult, are you going to experience a winery, and the ambience, or are you a connoisseur of wines? If you have a prefered wine that you drink, you may want to visit a winery known for cabs, The Russian River Valley is known for Pinots… For a dining experience, Charlie Palmers Dry Creek Kitchen in the hamlet of Healdburg… or the French Laundry in the Napa Valley. Sonoma County Winery Association has guide books that could help you… As well as Napa Valley. After you get some names of wineries check them out on line too as well as some of the restaurants, you can check out menues! I know I did not answer your question, I would just need more info to help. Enjoy your trip…