Not from SF but I did a ton of daycare/preschool shopping in Florida so my $0.02:
I was very impressed with Bright Horizons. They were the only "big chain" preschool that offered part-time hours & days that fit my self-employed schedule, even though the rates were a little higher than I was ready for but not outrageous. They offered swim lessons on site, free pre-K for 4-year olds (a Florida thing), meals were included, they did sports/gymnastics/dance on-site, and I met with the teachers who all seemed happy to be there. It was clean and I would have had no qualms enrolling our kid there, except it was a 20-25 minute drive away. It honestly reminded me of a nice elementary school, just with younger kids there.
We ended up going with a parochial school in our neighborhood (Episcopal), and we are not a member of the church, or any church for that matter. We grew up Christian but don't attend church regularly, so it didn't matter to us whether it was a religious school or not. Our daughter has attended Episcopal preschool during the year, Presbyterian toddler summer camp, and at one point I was going to enroll her in a Jewish preschool b/c they are highly rated and had the most flexible hours (it was just too far a drive). The church preschools are amazing and decently priced, especially for part-time working parents. If you can find one with wrap-around hours for full-time working parents, even better. Her preschool only goes to pre-K, and if it lasted K-8 I would pay for it in a heartbeat b/c we love it so much there. It's like Hogwarts for toddlers, and we can walk there from our house :) I also found that the church preschools were more flexible with things like age requirements, i.e. the "18 month old" class had kids that were 14 months, as long as they could walk & hold a sippy cup.
Best of luck!