After spending hours looking through all the tours to the Napa Valley, we finally chose Green Dream Tours. We were not disappointed. They weren't the cheapest, but I do believe that you get what you pay for, and what we got was a fantastic guide (Jake), a small (and perfectly formed !) group of just 5, some great wineries and an overall great experience.
The trip to the Napa Valley from Downtown San Francisco took approximately 90 minutes and this time flew by with Jake giving us a history of the area, both San Francisco and Napa Valley, in addition to an introduction to the wineries themselves.
The wineries were small and we immediately felt welcomed, however I never did feel pushed or pressured to make any purchases. The fact that I did purchase wine was down to the fact that the wine was damn good ! No more shopping for £4 bottles of wine in my local supermarket anymore !!
The only negative of the trip - the fact that it had to end. I would recommend Green Dream Tours 100% and would definitely use them again for my next trip to Californian wine country.