By "the hardest bodyweight chest exercise", I mean the one that requires the most amount of skill and strength. Is there a bodyweight chest equivalent to the handstand pushup or the front lever, for example? Thank you.
Well, if there is a "chest equivalent" to a handstand pushup or front lever, it's either a full planche or maltese. (or the push up variants of both exercises)
Both exercises require a lot more than just chest though, so they aren't JUST a chest exercise, but they require a lot of power and skill to perform.
I would say that of these two exercises, the planche push-ups require more power from the chest than a maltese, which is more shoulder power than chest. I have to add that I can't do a maltese yet so I haven't experienced the movement myself, but I've done some iron cross progression and I'm assuming the maltese is somewhat similar to that.