We likely don't know how the players actually are in terms of leaders in the room, so it is hard for us to say who would be the appropriate choice.
But McDonagh to me doesn't seem to be captain material yet, he seems to quiet and reserved. The same goes for Staal. Landeskog is young, but he is a natural leader and has that intrinsic confidence and charisma.
I've thought about Zuccarello as he is perhaps the player that embodies what I want to be the AV Ranger: skill, intensity, work ethic. But while he is a popular guy in the room, I think he is a bit too awkward to be captain - not to mention the lack of NHL experience and credibility. He may become an NHL captain in his later years though - it is not outside the realm of possibility.
Stepan is definitely captain material, but I think he is currently too focused (and rightly so) on developing himself as an NHL player to be a captain. If he was just continuing on from last year's level of performance he'd be a good choice, but this year shows he isn't ready for a leadership role yet - he needs to sort himself out first.
Girardi is probably the best choice IMO - if he is given a long term extension. He seems to have that natural confidence I think is very important for a captain and while he may not be the most vocal guy in the room he doesn't strike me as shy at all.
I emphasize natural confidence as people who has this can lead well even if they struggle on a personal level. A guy with his heart on his sleeve may be sympathetic and likeable, but is probably not the best leader.
Nash, and especially Brad Richards, (and Hank for that matter, though he isn't a realistic choice) are not good choices for captain for this exact reason. They have shown to me that they easily lose confidence and are very hard on themselves when they struggle. Hank definitely doesn't have the ability to care for the rest of the team while he himself is struggling. His strong focus is one of the things that makes him great - and also what disqualifies him as captain material.
On the opposite side we have Carl Hagelin who seems to have an unbreakable confidence. But he isn't established enough and doesn't have a big enough role on the team to be captain - even though I think he has the right mentality.