I'm definitely happier in startups too. Being in the middle of a startup with traction [1] keeps you sharp. I tell myself that it also makes me more valuable in either a bigco or another startup.

At some point though you need to seperate the emotional from the rational. And building up career qualifications in challenging startups stops meaning that much when you lose sight of any ways to deploy those qualifications down the road.

[1] Important qualifier.