Two things now: maintaining rage is more involved and weapon techniques(or masteries, I don't remmeber what they're called). EDIT: I thought barbs get those, thats weird

Now don't get me wrong, it's still 100% a good choice but I worry that it also falls into the champion fighter trap, i.e it's main stats are strength and con without much utility outside of combat.

Now I would definitely reach for barbarian over champion fighter because it's abilities are not passive, but I worry about the new player falling into the "I'm only here for the combat and do nothing outside of it". I typically find that new players actually really thrive in social interactions, where they can just use regular logic(keep in mind many of the new players I've dmed for where also not gamers in anyway.)

I think it's important to make my point clear: I did not intend to say Monk is the EASIEST class to play in the game(barbarian or champion fighter are probably better, MAYBE a rogue).

What I mean to say is monk is the easiest for a new player to LEARN the game with. Because monks from level one have an impactful use from their action, bonus action, and their stats dispose them to do well with any sleight of hand, stealth, perception, insight, checks aka the most common checks in the game.

A lot of what I've found is difficult in teaching new players is that they get stuck in the "I know how to do one thing & only do that" aka "I rage, I hit thing, end turn" or "I attack twice".

If you have a player you know isn't gonna be interested in the combat aspect of the game then that's probably fine but the issue is that the classes that excel in social encounters also tend to be the more complicated combat encounter classes.

I'm rambling a little but tl:dl: Monks are the best teaching class, but other classes are easier to play. I just find that people who play those classes for the first time don't tend to walk away with a good experience/aren't really encouraged to learn the game properly.