just saw your other thread..
if its only you and the g/f, stay at the JW or Stanford Ct.
I would do an organized city tour (3-4 hours). they will take you around, maybe make 1-2 stops. You will get to see most of the city. You can then go back to the places that interest you most, like Chinatown, Wharf, etc. You dont need a rental, unless you head up to wine country. Parking is expensive, $40-60 nights, so keep that in mind.
As far was wine country, I prefer Sonoma. Less tourist, smaller wineries, most family run and tastings are usually cheaper or free. However, if this is your first trip, Napa might be worth checking out. You can either drive yourself or hire a driver. I would stay away from tours and just research yourself which wineries to go to. If you are limited on time, pick a particular varietal (Cab, Chard,etc) that you like most and research those. I would only go on one Tour, as they are pretty much the same. After that, hit the tasting rooms. If you plan it out, you can hit 4-5 in a day. Also research what time the places close. I usually end at Chandon in Napa, as they stay open the latest and are closer to SF.
Just some thoughts. If you have any questions, let me know! i lived there for 5 years and went to Napa about once a month.