I much prefer thinner bits - horses mouths weren't made to accommodate a metal bar so I believe a thinner bit is more comfortable sitting passively in the mouth. I can't stand those huge hollow bits that don't even allow for closing of the mouth or proper swallowing.
Thinner bits can have more bite but they are also more refined. I ride all my horses, even my young breaker, in thinner bits. As long ad you are concious of your hands it isn't an issue.
So it isn't as simple as thin bits are harsh and thick are mild - I always bit so that my horse is as comfy as I can make it when the bit is sitting passively - I want them to be able to carry it comfortably because that is the reward when pressure is lifted.
I should also add that I don't agree with wire bits.
My ideal thickness if it suits the horses mouth is the thickness of a Myler mouthpiece. Posted via Mobile Device