If going to a startup, do you have a desire to be the CTO, or a key contributor. If CTO, or top person in charge of the technology, you will learn a lot about how to run the company. If as a key contributor, it will depend on how many are on the team, as if you aren't working core with the founders themselves, it will usually feel like a normal job. Not that that is a bad thing, but just usually the reality.