Comment by JeremyNT

This is really where the focus needs to be for young people, and I think it's where our education system is really failing.

What exercise is best? Why... the one you enjoy and will continue doing!

Focusing on ROI can be a good way to view it for the right personality type, but I think that mentality can be harmful for the wrong personality type who will just grind out activities they don't really enjoy until they give up in exasperation.

I suspect for most people the trick is just finding something - anything - that is physically demanding that they enjoy, and then sticking to that.