Ask HN - Work Progression and Start-up Dilemma

Current Employment Situation: I am a senior developer on a team of about 25 other developers, and lead a team in the development of our core system. Work is decent right now but majority of my work is really on overseeing some of the other developers and helping with projects that are behind schedule ramp up to speed. The challenge is more on managing personalities rather than my own development skills. I would be promoted to a more senior role very shortly. I would rate the work as about 6/10, love having fun with most of my co workers, but I would love to work with some "A Type" players instead. Other Employment Opportunity: I also have opportunity to join a company that is more innovative and business oriented. The work will be more focused on emerging trends (which I love), a bit more prototyping and understanding opportunities and work with what I believe to be more "A Type" players. I suspect the demand physically and mentally would be much greater. I have excellent trust and respect for each of my manager in both scenarios. I also have a strong desire to pave my own success and work on a start up which I have done so thus far by working late at nights. Until my start-up is at a state where I can launch and be profitable, I would still like to be employed and potentially grow. Beta could be in a couple of months. Which option should I take and why? This will certainly help me out in making a decision.