I see you're writing from the Inner Sunset. I used to live in this neighborhood so I know it quite well. I both drove downtown and took the muni
as well - specifically, the N-Judah train, which is supposed to be one of the more frequently run lines in the city.
Driving took about 30 to 45 minutes consistently each day. Muni fluctuated from a minimum of 20 minutes to a maximum of 90 minutes at times. Of course, you'd have to factor in that you have to pay for parking in some cases and gas. However, the Muni fare, while inexpensive by comparison, comes with the externalities too - i.e., other passengers etc.
Thinking about it as a realtor, commuting and access to public transit is just one factor in the mix. Like the Muni, inconsistency and variety is the name of the game. Sometimes clients don't care, other times clients want to as far away from a Muni rail line as possible and others insist upon being near to Muni or Bart. Most realtors will focus on a location's Walk Score instead. Take a look at walkstore.com to see and 511.org. Hope that helps!