When I graduated, Google/Amazon/FB/MS, I knew people were smart and the job would be okay at the very least. How should I have gone about figuring out which ones are "a startup with smart leadership". I remember being overwhelmed by everyone, everyone came across as smart.

So I counter your advice by saying the best opportunity for a young engineer is likely a large company that is well-known for having generally smart people. At least I learned what I wanted and didn't in the rest of my career.