Both San Francisco and Los Angeles have their own charm. You will live well in each city with 3 million. I would choose San Francisco.
Best towns around the Bay Area
1. Hillsborough, CA
2. Belvedere, CA
3. Atherton, CA
Weather in the Bay Area December-February averages about highs-lows 63-45. And March-November is 73-55. There are about 300 days of sun. San Francisco is a beautiful city with very excepting and beautiful people. Beaches in Northern California can get a little bit chilly, but there are some of the most scenic biking and hiking trails in the US. But nobody dislikes SF, afterall there is a reason why 5 of the top 10 localities to live in the United States are in the Bay Area.
"One day if I do go to heaven~
I'll look around and say, 'It ain't bad, but it ain't San Francisco. "
Herb Caen
Best towns around the Los Angeles Area
1. Malibu, CA
2. Beverly Hills, CA
3. Lauguna Beach, CA
Weather in the LA area December- February is good. Highs-lows are about 70-45. March-May and October-November high-lows are 80-55. June-September high-lows are 90-60. There are great beaches in Southern California. You get about 320 days of sun a year.