If you're talking about tech skills then I'm a Python guy. I would also like to get into C or C++ at some point. I am trying my hands at Django now, and I'm not totally sure how I feel about it. I hear that Rails is better for web development, but it doesn't scale well.

Aside from that, I'd love to have a project that I have a lot of influence over. That's not something you can easily get at a company like Google.

I'm talking about everything else. The habits and thinking you'll develop. The way you'll learn to work and interact with coworkers/customers. The things that will motivate you. The way you'll be rewarded or punished. And a bunch of other things.

The environment of a well run big company and a well run startup are very different (for good reasons). You don't learn to succeed at one by working at the other.