If you’ve taught in Universities and in secondary school in America, what were some of the biggest differences between these two work environments and which did you enjoy more?

I've been reading a lot on how in America people with PhDs and Masters in both the sciences and humanities can't get steady jobs teaching in Colleges so they've had to teach in secondary school. So if you've taught in both Universities and in secondary school or know people who did, how did these two work experiences compare?