PhD, Startup, or Career? 
noodle: i'd suggest you sit down and take stock of what you need, first.  if your situation requires you to follow a specific path, do that.after that, figure out what you want, and follow that.  you have time and little obligations (i'm assuming), so even if following what you want to do leads to a dead end, you have time and flexibility to get past that that you won't later in life.