I'm not sure I'd laud startups for 'career security'. Outside the valley echo-chamber, few companies have any respect for startup experience. ('startup' sounds a lot like 'small company' if you aren't a hacker...)

Also, for every startup where young employees get a chance to punch above their weight, there's another where the devs grind all day long on customer support issues and maintenance.

On the whole I'm personally more inclined toward startups than large companies, but I've been around long enough to be wary of mythologizing them. They have their own set of dysfunctions that can be as stressful as anything you'll find in a bigcorp.