I can see advantages for each: I think I would like that environment better at a startup. From what I hear you generally get a lot more freedom. You hack on cool projects that you are passionate about, but you work hard, which I don't mind. On the other hand, I think that working at a larger company would help me learn more. There would be more senior developers that can provide insight whereas in a startup there would only be a couple other developers, depending on how far along the company is.
What I'm looking for is some insight. What have you learned from your experience? What are the pros and cons of working at a startup versus a large company? What do you recommend for someone looking for their first internship?