For reasons I don’t understand, Google Maps doesn’t seem to know about the Golden Gate Transitbuses, even though there’s a whole bunch of them and they are by far the fastest way to get from downtown SF to the Cow Hollow/Fillmore/Presidio area on transit.
There’s a whole mess of bus routes, but the most interesting for SF residents who don’t need to commute to Marin County are the 10, 70/80/81, and 101/101X. These run from the Financial District (1st & Mission/Transbay Terminal) to Civic Center, then up Van Ness and west on Lombard. Because they make limited stops, they’re fairly fast (though at $3.75, more expensive than Muni). For example, from my neighborhood of Glen Park it would take over 45 minutes to get to the Cow Hollow area on BART+Muni (on the 22-Fillmore), but only around 25 minutes on GG Transit, which is competitive with driving once you factor out the time needed to try to find parking in Cow Hollow (good luck).
And if you have friends in town who want to see or walk across the Golden Gate Bridge without the hassle of driving there, taking these buses from downtown SF is an easy way to do it.
They run pretty late, although outside of commute hours they run infrequently (once an hour for most routes), so you have to plan ahead a bit.
Downsides: they don’t appear to be on Google Maps, so you can’t get transit trip planning that includes them (511.org has a trip planner that does include them, but it’s horrible and inaccurate); they don’t appear to be on NextBus, so if there’s traffic you won’t have a way to tell how delayed they are.
Still, it’s better than taking the 22-Fillmore all the way out there, and certainly better than trying to park in Cow Hollow.