bits. the soft tissue (tongue) handles pressure & is able to "bounce back" to the original form. on the other hand, the hard tissue, or the bone of the face, cannot give to pressure or bounce back. the face also has many more nerves & therefore is more sensitive to pain. if you pull too hard you can easily damage the cartilage. if you place it too low, you will restrict breathing. with a bit, the horse can move it up in their mouth or choose to evade pressure. with a bitless there is no way for them to relieve pressure or hold it where they want it. ive also noticed that when someone uses a bitless bridle, they have harsher hands because they don't think they're causing the horse pain, but in reality they are causing more pain that if they were using a bit.
I think it totally depends on the horse. If a horse prefers going bitless, go bitless! But if you’re horse is perfectly happy in a bit, keep riding in a bit.
Bitless bridles can but a lot of pressure on the nerves on the face and it’s important to realise that riding bitless isn’t necessary ‘kinder’. Everything depends on how it’s used. If you ride with a Pelham and yank your horses mouth, it’s gonna hurt. If you ride in a hackmore and pull hard it’s going to hurt.
So whatever suits your horse
I believe it depends on the horse and rider and if he or she is using it properly. These days everyone has different opinions on everything, even scientifically proven facts. But the right rider I personally prefer bits. It’s a more direct specific tool that gives a concise response.
I much prefer bitless, since it proves that horses can be ridden without a bit and doesn't interrupt or affect the horses jaw movement or ability to breathe. Horses mouths were made for eating, grooming and investigating new things - not to endure the presence of a weighty metal bar.
There's so much evidence that horses do not like bits, yet people still continue to use them in order to gain 'control' through pain. Evidence includes head tossing, mouth gaping, the need to use a flash noseband, having to make the horse open his mouth to take the bit, etc.
Bitless riding allows the horse to have freedom in his mouth and takes away the need to use a metal bit in order to make the horse do as he is told through a metal pain device. Instead, bitless bridles and pieces, such as hackamores, rope halters or the Dr Cook bitless bridle focuses on using pressure points around the horses face to communicate to the horse.
Well, that's my opinion for you and I hope it is put to some use for your project! Good luck with it! :D