Marcurio has some of my very favorite random dialogue.
However I just started using a multiple follower mod, I'll have to play a bit and see if I hear random stuff from all of them or just one. It's an interesting question and one I never thought about before. If only one follower at a time can generate random dialogue, I wonder what decides which one? Is it the first one you asked to follow you and anyone who joins after just keeps their mouth shut?
Seems like I've heard both of my two current followers shouting their combat dialogue in battle, though. OTOH in battle situations pretty much everybody yells stuff constantly anyway.