I founded a startup that failed and then worked for Google for 2 years (and counting...). I'd say they were about equal in terms of personal growth and development, but taught me very different things. Failing at a startup taught me a lot about myself, what I really value and want to do, what my tolerance for ambiguity and stress and risk is, and so on. Working for Google taught me a lot about the world, what other people value and want to do, user expectations and how they'll never be satisfied, plus a whole bunch of technical skills. Hopefully, combining them together means the next startup will succeed. :-)

It doesn't have to be an either/or. There's plenty of time to both fail at a startup and work a couple years at Google.