I know families at all 3 (slightly different) and have played one or both sports. Z and SJ different especially re football. If you aren't recruited to play there are very low odds your son will ever make varsity. There is very little overlap - maybe none - of key players on the football and lax teams. Their best lax player, Ryan D, was their place kicker and gave it up a few years ago. Zaga has a lot of kids that play both sports at varsity level. So if your son is good at both, but not a phenom on the grid iron, Z may be a better fit.

Prep football is okay and has decent overlap with lacrosse. I don't know percentages, but kids play both particularly early in their HS adventure.