From personal experience and from what I 've heard here and there, you have to know what you ' re doing when using a hackamore. It can hurt the horse if not use properly? Not sure, just heard it from someone.
I believe bits are better than bitless or hackamore, just because that's how I rode my whole life, that's how I broke, or known horses to be used to. You have more control, and more options.
Now, if there is some mouth issues like someone said, hackamore is probably the best way to go or bitless bridle.
But there is obviously less control so you have to be more careful or know your horse really well that you are sure he wont take advantage of it
I think bits is the best way to go, there are some really soft bits if that's what ur looking for,
Again, like people already said, it depends on what you want out of it? Does your horse has issues? Or are you just brainstorming in a new way to go with your horse?