旧金山 is more commonly used in mainland China, people from Hong Kong and a few southern provinces use 三藩市

Actually after thinking about it a little more, I think the term 三藩(san fan) came about because it phonetically sounds like San Fran. 市 means city btw. Similarly, New York is called 紐約(niu yue), and Canada 加拿大(jian a da.)

Yeah, the reason I asked is because my parents call SF, seeeh feeeeh zzzz, in Shanghainese; and my friends call it saahm faahn si in Cantonese. So i guess that would be equivalent to calling it san fan shi in Mandarin. I've never actually heard of it being refered to as jiujinshan until I looked it up on the Google Translator.

三藩市 was used in Hong-Kong and some southern chinese area. now we call the city 旧金山 or 圣佛朗西斯科

舊金山San Francisco