PhD, Startup, or Career? 
jeeringmole: I went straight to graduate school, heeding advice that it would be difficult to give up the comfort of a real salary for a grad student stipend if I went and worked first.  I observed in grad school that the students who had done that knew why they were there and what they wanted far better than I did.Fundamentally, you will only know in retrospect whether or not you made the right decision.  On the other hand, the stakes are not as large as they seem:  5 years is 125% of your time as an undergraduate, but only 12.5% of your career.  (In other words, you have time to switch courses later, though it may appear now that you don't.)Finally, the advice I always repeat to people facing difficult decisions.  (Anyone who knows where this came from is welcome to tell me.  I would attribute it if I knew the source.)  ....  When you have a difficult and important decision to make, flip a coin.  Not because flipping a coin is a good way to make important decisions, but because in the moments while it is spinning in the air you will know which way you want it to land.Trust yourself, good luck, and congratulations on earning such a plethora of attractive options.