Honestly the smartest thing you can do is ditch the car rental counter completely. Bart blue line from sfo straight to powell street (downtown) takes 34 minutes for $9.65. Trains run every 15 minutes during rush (4:30-8:30am, 4-7pm weekdays) and 20-30 minutes otherwise. Pro tip: avoid the first car, it's always packed with airport luggage chaos.

Grab a clipper card at the sfo bart station before you board - loads cash value and works on literally everything: muni buses, cable cars, ferries, caltrain. The mobile app exists but the physical card is way more reliable for tourists who don't want to deal with dead phone battery disasters.

Why no car? Parking downtown runs $35-60 per day minimum. Sf's hills will destroy rental car transmissions (seriously, i've seen tourists smoking their clutch on lombard street). Street parking requires a phd in deciphering 47 different signs that contradict each other. Plus traffic makes a 2-mile trip take 45 minutes on a good day.

Muni day pass is $13 digital and covers everything. The f-market streetcar hits all the tourist spots along the embarcadero. 38-geary runs straight to ocean beach if you want to escape the crowds. Cable cars are included but expect 20+ minute waits - they're basically slow-moving instagram props at this point.