To add to Sam's take, I'd say the real benefit of joining a startup is the opportunity to work closely on a problem that you care about. Do you want to expand your POV and learn new skills? Do you want a high-degree of personal responsibility for your work? Your role will change every 6 months, as the company's priorities do.

Compensation and relationship dynamics are crucial, of course, but your success and experience will be largely determined by how much you want to take ownership for your work.