For me people trumps nature. I like living in a big international city with a lot of culture, getting to meet a lot of new people all the time. At least not being closed off to those possibilities.

It doesn't have to be SF. It's not just that rent is expensive, it's that for the price you pay you most likely aren't even living in a nice neighborhood (most parts of Mission, parts of Soma, Market, parts of Haight, Divis, most of Western Addition, Lower Nob Hill, etc. - these aren't nice places at all for $3500/ month, which would put you in the very best areas of pretty much any other city in the world).