Find the fairest place to meet on the Paris Métro

When I lived in Paris years ago, I worked near Gare du Nord, but my friend Jenny lived near République. If we wanted to meet up after work, we'd just meet halfway along the Orange Métro line, around Gare de l'Est. Easy. Since that's within walking distance we wouldn't actually take the Métro, but Métro stations are useful waypoints in Paris even if you're travelling by foot. But when we wanted to meet with our other friend Eric who would travel from Porte de Versailles, it was tricky to find a mutually-agreeable place to meet, so that we'd all be...