My mare was started in a happy mouth loose ring snaffle, simply because you never want to start something in a strong bit cause it will make them harder in the mouth. Now just cause you start them in such a soft bit doesnt make that bit the "one" for them. You can change it when they get older. But why not start them in a soft bit like that so they learn to like the bit and maybe they will never need a stronger bit in their life
A cavesson (riding model :P with a plain nose-iron, no joints or chains) and after that a muserola (pretty much the same thing but without the extra ring on top of the nose, and it's put in the regular bridle).
Because that saves his mouth completely untill he has learnt to listen to the rider and reins. It's not more gentle on him, but the mouth stays sensetive and it's easier for a young horse to understand preassure on the nose (since it's already used to a halter and has learnt to stop for that) than in it's mouth.
Then we rode with a muserola and a spanish curb together for a while, to teach him a few things about yielding (again, a curb is easier to understand when it's about yielding forward and down for the rein, while a snaffle or muserola is easier for stopping and flexing, which is why no horse that's not very well educated should have a curb/shank/hackamore alone).
Now he's ridden wih a regular snaffle. Or a halter.. or a riding cavesson.. or the curb, or the hackamore....or whatever I feel like. But usualy thew snaffle or the halter.