If you are going to visit Wine Country from San Francisco the easiest way to get there and do some winery-hopping is by car. Apparently there are some buses and trains you can catch too, but once you get to the main towns, public transport options are scarce.
There are numerous car rental options available, and most offer similar rates and types of vehicles. We ended up hiring a car from Avis, mainly as we got a discount through our AA membership.
Collecting the car from downtown San Francisco was straightforward, and they gave us some helpful maps and some brochures about things to do on our travels. We found the drive up to Wine Country easy enough using the maps and following the adequate road signs.
At the end of our driving adventures we dropped the car back at San Francisco Airport, which was an amazing set up. It took about 30 seconds to return the car and we were on our way.
If you're traveling from San Francisco to Sonoma, the fastest way is to rent a car. Take Highway 101 North, across the Golden Gate Bridge and into Marin County. Then take Highway 37 East and Highway 121 towards Sonoma and Napa. Follow the signs to Sonoma. It's a scenic 1-hour drive.
It is possible to make the trip by bus, but it's a lengthy process: you would need to take Golden Gate Transit to Petaluma or Santa Rosa and then take Sonoma County Transit to Sonoma.
Since the Sonoma Airporter ceased operations in October 2009, there has been no direct airport shuttle service between Sonoma and SFO. The closest shuttle is Sonoma County Airport Express, which runs from both OAK and SFO and stops in Petaluma and Santa Rosa.
Sonoma town is located 80km north of San Francisco, we used an organized tour that took us to three different wineries but also made a stop here for lunch.
If you don’t want that you can easily drive here in about 50’. Just cross the Golden Gate Bridge and then highway 37 east and Highway 121 toward Sonoma County, then just follow the signs :) The car will give you freedom to explore around and enjoy the scenery much more. After the wine give the car to someone else please! :)