1st time visit to San Fran. Napa or Sonoma Valley?

[Nina]

Hi,

I will be in San Fran in a couple of weeks (first time visit) but I will only have a day or two to visit either Napa or Sonoma. I think we'll be renting a car but I don't know which one to visit, Napa or Sonoma. I am knew to wine (I don't even know which kind I like yet) but I would like to get some input on where I will enjoy the most and get the most out of.

Thanks,
Nina