Oakland or San Francisco Airport ?

We're planning a trip to SF and area in April so I've been following all the
various newsgroup posts with much interest. Many good suggestions on hotels,
restaurants, things to see, websites to visit first. One thing that no one
seems to have discussed is the advisability of using the OAK or SFO airport.
Or does it make any real difference? We're going to spend our first few days
in the city then rent a car and head down the coast or out into the valleys
for another five days. Best fares seem to be into Oakland.
Thanks.