If you have good grades in demanding courses but attend a highly competitive high school, college admission officials will be aware of this competition. So you should not shy away from a strong high school for fear that you will not stand out academically.
However, if the average SAT score at the second school is 60 points lower that at the first, that’s no reason to pass up this school. It doesn’t mean that YOUR scores will be 60 points lower. If this school isn’t as competitive as the other one, there may be more weak students there bringing that average down.
It’s a bad idea to choose a high school based on these factors. Instead, consider which school offers an environment that suits you best or which provides other attractions for you (e.g., better sports or better orchestra, more convenient hours or location; a variety of special programs). Ask students at BOTH schools what they like—and don’t—about their school.
Then ask yourself this: If you had already been guaranteed admission at your top-choice college, which one of these high schools would you want to attend? That’s the school you should choose!