Payment gateways can be a problem when your company is not US-based.
Paypal, WorldPay, ...
There's the obvious allure of Silicon Valley given the investor/startup culture there. I suspect the question was probably more focussed around SF than the US in general.
Just to clarify.
I am in currently in the US in Boston, MA.
And yes I am more interested in the advantages and start up culture of Silicon Valley and SF
OP is apparently currently in the US. "Start where you are now" is a good rubric for most things.