Probably public school.
I'd want my kids to have more of an Islamic education than just a class on a Sunday morning though. I went to public school, and had madrassah and Urdu class every weekday after school (just saw my Qur'an teacher yesterday after years and years; it was pretty cool. Dunno how he recognized me.)
Would you be more worried for your boy children or your girl children though?
One of my friends (used to be really bad in high school; did a total turnabout and is an amazing person now with a solid religious education, MashaAllah) said how he thinks it's easier to discipline boy children though, as compared to girls. His reasoning is that you can hit the boys (chappals and belts apparently

) but you can't hit your girls.
I think it's the other way around. I've seen more boys go bad than girls in public schools though. Drugs are very readily available and... yeah, young men are just more susceptible in my opinion.
My parents' solution was to send my brother to a military boarding school. In Pakistan.

But they kept me in the public school system, 'cause they know I'm not gonna do anything stupid.
So maybe for the boys, if you don't want to send them to a military school: beat them every so often. Even if they haven't done anything. Preemptively.
Seriously though, I think if you instill an Islamic foundation in your child, communicate with them openly and give them a little bit of your trust and a little bit of their freedom, they'll be okay. Kids are going to be kids and InshaAllah, I won't get mad at my kids for little experimentations. Just a little bit of leeway... and a lot of love and understanding.
Oh, and I started working at 17, but after years in the public school system, it wasn't a shock. 'Cept for getting used to calling older colleagues by their first names instead of "Mr." or "Ms."
Out of curiosity though, what're you guys worried about? I mean, what is it that your hypothetical kids are going to be exposed to in public schools?
