I have an army of extremely mild bits for the TB I’m riding, and we’ve had the best luck in the Stubben Golden Wings loose ring snaffle. Something about the construction of the bit makes it easier for me to keep contact and for him to maintain it. I don’t know exactly what it is that makes it milder than my other bits.
Unfortunately, it’s not dressage legal, last time I checked, because the “wings” are considered bit guards. But it is a lovely and very mild bit and I plan to ride in it for a while and then move on to something I can show in.
I also like the Stubben EZ Control bits. When you pull back on both reins, the bit “locks” into a solid piece, similar to a Myler, and does not completely collapse/fold like a traditional snaffle. This prevented the TB I’m riding from being so fussy with his mouth.
We tried the mullen route, but the Happy Mouths, etc did not agree with him like these other ones did. I think it’s an individual thing for the horses, plus has to do with our hands, riding style, etc.