According to Time, the city that takes the most selfies per capita in the world is Makati City, Philippines. San Francisco came in at #11 with 91 selfie takers per 100,000 people, a number I find surprisingly low.
Time's research included deciphering the location of 400,000 Instagram photos tagged "selfie" that had geographical info. I'd argue that this casts some doubt on the research based on how ubiquitous selfies seem and how infrequently people include their location. And do people actually add "#selfie?" A visible forearm pretty much gives it away. You can see the full methodology at the bottom of the original post.
Some other interesting cities on this list include Oakland (#27) and Anaheim (#4 probably 'cause Disneyland selfies are a thing). You can view the stats of other cities on Time's interactive map.