Why did I go to SI Tech? I got into Stuyvesant but I didn't want to commute to Manhattan every day. I felt that I would miss out on all the extracurricular activities if I had such a long trip home. So I went to SI's magnet public school instead and never regretted it. It's a small school that is rather hard to be accepted into, but if you are it's a wonderful environment to learn in. You never feel singled out as a geek or a nerd (because we all were geeks and nerds) and since Staten Island teachers fight to be posted to Tech, you get great experienced teachers.
Also, their exchange programs to Russia are superbly run. I spent a month in Moscow in '95 and will never forget it.