What is the kindest bit for a horse?

Could you please elaborate on what you mean by "kindest bit for a horse"? Are you referring to the most comfortable or humane type of bit for a horse's mouth? Or perhaps you're asking about the best type of bit for a particular purpose, such as training or showing? In the world of horse riding and training, there are many different types of bits designed for different purposes and horses, so the answer may vary depending on the context. Could you provide more information so I can give a more accurate answer?