From my perspective, Founder or Co-Founder is kind of parallel to your position in the company. It usually (but not always) indicates the company is too small to have actual job descriptions OR is used with your title to indicate you're one of the founders. eg Founder, CEO or Founder, CTO. It helps others (investors for example) give a sense that you are more than an employee.
Entrepreneur is kind of like saying "business owner" and sort of more generic. I would not use that with investors - it's not specific enough.
I know that's sort of vague, but that's what it brings up for me.