My Templar and I have an arrangement - "till death do we part, and even then just until we respawn." We've been through a lot, but I can always count on him to throw a heal on me if the demons have been getting me down. Well, not always...always...
I've more or less left the other two followers in town for most of the game. I don't really have any intention of taking them anytime soon as well. I talk to them, of course, and get all their dialog options, but it's just not the same.
Are there any achievements or custom dialog that I can only gain by spending more time with other followers, or taking them into specific situations?