I just took BART from SFO to downtown San Fran yesterday.
More things to consider.......
Per person fare is $4.95 to the 4 main downtown stations. Travel time is 30 min. Large amounts of luggage are permitted, but it can be very hard to hail a cab outside any of the stations except Embarcadero (go to the Hyatt.).
So, unless you're a sherpa or were a pack animal in a past life, make sure you understand the distance from BART to your hotel.
Also, a large percentage of the route is in a subway and good scenery is quite limited.
Another option is Supershuttle and the other shuttle vans. They cost a bit more, but are door to door and you'd see some sights on the way in.
So for me, if I were visiting for a cruise with lots of luggage, Id take a van. If I were traveling light, and did't care to ride through a tunnel, BART wins.