This question leads me to believe there are a limited number of people in the company. With that said, and I mean this sincerely; why do you need a title? If you are a key person in an early stage start-up what will the title do for you? Will it pigeon hole you into a specific role or skill set when you are responsible for so much more?
One more question; Did you mean the right title for [responsibilities] in a startup? If not, please explain what a "startup title" is?

That's 3 jobs: Marketing manager, Biz Dev Manager, and Product Manager