The former - focus your initial time on building, getting users and feedback. If all is great, you will have a number of options, including going to SV.
Is there a specific reason why you want to go to SV first?
IMHO, where you right now, I don't think that's a significant enough advantage. The costs of moving and living/working in SV is just not worth it at this stage.
Is there a specific reason why you want to go to SV first?