I am a veteran of both places. Here is what you need to know.
- NYC is 30% more expensive than Silicon Valley / SF
- you don't need a car in SF but you probably do in SV
- you might need a car if you live in the inconvenient neighborhoods of SF.
- the bay area is sort of automatically healthy, you have to work hard to be unhealthy
- NYC is automatically unhealthy, you have to work hard to be healthy
- the weather is better in California
- the women are better in NYC
- if you are decent looking and have a job, you can get a date in NYC
- you can be good looking and rich in SV/SF and still never get a date
- there are better options for outdoors activities in California
- anything besides outdoors activities is more convenient in NYC.
- hedge funds / finance can be more interesting than a dumb startup and will certainly pay more
- working for a dumb startup is bad for your career
- you can get trapped in a startup career spiral in SF/SV where you never make any money, even if you're a great programmer
- you'll eventually make decent coin in NYC even if you're only an average programmer
- there are interesting people in NYC with varied careers ranging from UN analyst to fashion designer
- in SF/SV there are tech industry people and weirdos
- counterintuitively, even though NYC is more money
oriented, the programmers often have very interesting outside interests. the meetup scene in NYC is intellectual, there's math, machine learning, functional programming, etc
- in SF/SV most of your fellow programmers will only claim road cycling and guitar hero as interests. the meetup scene is usually about source control or social media tweeting
I could go on and on. Thinking about where the best place is to build your startup is kind of silly. You want to think about what you want to build, and build it. You can always move later if needed. These lists are also dumb, although it was fun to write. Really the only way you can decide where to live is to experience places yourself.