Working for a large but still quickly growing company has been, for me, the best of both worlds. There's still a lot of upside in stock options and in career path because of the growth. You get to dabble in politics and you have a large community of people to learn from and keep in contact with in the future.

And usually, these companies are not mired in the large and unwieldy bureaucracy that is common in large and established companies. i.e. companies like Facebook, Zynga, Google 5 years ago, etc.

However, my experience is limited to two big-but-growing companies, one startup, and one small but completely dysfunctional. Too small a sample size for definitive generalization.