When choosing a bit for a green horse, it's important to consider his level of training and experience. A simple snaffle bit is often a good choice for young or inexperienced horses, as it is mild and easy to use. You may also want to consider a bit with a wider mouthpiece or a rubber or plastic bit, which can be more comfortable for the horse. As your horse progresses in his training, you can experiment with different types of bits to find the one that works best for him.