generally speaking, supposedly the thicker the mouthpiece the kinder the action, that said all horses mouths r different, my horse 4 example has a big tongue & was really uncomfortable in a thick snaffle. she is not strong & has a very soft sensitive mouth but is ridden in a pelham because it allows her to sit some of her tongue up inside the port so she dosent have to contend with a big chunky bit as well as a big chunky tongue! x