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My two favorite bit brands are those made by the Mylers and Mikmar. Both companies were created by horsemen who were interested in refining a horse's way of going by improving rider to horse communication. When a company's motto is, "Designed With the Horse in Mind," you have to think their product is at least trying to improve on what else might be out there.
Right now I am only using the two Mikmar bits; the combination bit is the one I use for trail work, and the eggbutt is for dressage. It is show legal as is the Myler french link. None of the other bits I own are legal for showing dressage, but that doesn't mean you can't school or ride in a bit that your horse likes. Use what works!
I know the combination bit looks a bit ... extreme, but Speedy G really travels well in it and seems pretty happy. Back in the day, when I only used Kimberwicks 'cause that what everyone else was using, I would have thought this bit was horrifyingly atrocious. The truth is, the string over his nose gives him a signal that I'm asking for something, the width of the mouthpiece disperses the pressure over his tongue, and the three pieces of the mouth piece allow me to use each side a bit more independently of the other. Oh, and the roller is just for fun!
The Lozenge bit makes him more comfortable than with the French link, but it doesn't send my cues quite as effectively as the combination. Interestingly, he did really poorly in the French link. With the reins attached to the loose rings, the message he got was "WTF?" There was too much movement in his mouth with the ring slipping round and round, and the flat link of the mouth piece put pretty sharp pressure on his tongue. It was actually trainer number 2 who suggested the move to an eggbutt bit. Speedy G thanks you!