The dressage trainer I've worked with for the last 5-6 years starts and continues to ride all her horses and her clients horses in a french link loose ring type snaffle, and only switches to a different bit on those horses that are advanced enough to start riding in a double bridle, and even then most of the work is still done in a french link loose ring. It sits in the horse's mouth better, as mentioned before, and is a lot softer on the mouth than a lot of bits, but you do have to keep in mind, that any bit in the wrong hands can become severe and painful. In dressage you like to encourage chewing while the bridles on, and all the horses I've worked with in the french link seemed to like it better than what they were started in originally, if my trainer hadn't started them. I much prefer the french link loose ring, but I do keep an open mind that some horses don't work as well in it as others, based on their mouths, and conformation, and what they were started in ect. I do not believe that there is any "perfect" science to one "perfect" bit for every single horse out there, but there are some bits that just seem to work better for a wider range of horses than others.