Do you prefer a mugging or a traffic jam?
I'd say NY -- more community, more arts, more cool parks, museums, etc. etc...
Air quality sucks both places... traffic is bad in LA as well as NY, but at least in NY you don't need a car... I'd say there are more young people in NY -- at least it seemed to me that way. Most of the nicer places to live in LA are full of fake people who adopt their personalities off the latest hot TV show. The nice thing about LA is that most of the adult industry is at your doorstep. If you think you are going to be "discovered" in LA -- that's why most people move there -- don't get your hopes up... Of course I'm no expert -- that's just my opinion ;)
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...from the nectar of the Bone flows all that clicks...