They are (in most cases) interchangeable. If it needs more emphasis, you should always use 'jij'. Also when pointing out to someone.
"Ik wil geen menu, maar jíj wel!" (I don't want a menu, but you do!) "Wie is de beste? Jij bent de beste!" (Who's the best? You are the best!)
In these cases, 'je' wouldn't make sense. If you say 'Je bent de beste', that's a perfectly correct Dutch sentence, but it is just stating a fact, no emphasis.