If you haven't done these yet, do both. Millbrae has a cute little downtown, great bus connections and great Cal-Train connections. There are lots of nice places to eat and have a romantic evening away from the City. SFO has a grat little sushi bar in the food court right after you get off the train in the international terminal. You can have sashimi and drink a Kirin while chatting with business people on the way to Malaysia and Hong Kong.