btw, I’m a bit-a-holic… just so you know. 
How about bit material- has anyone really noticed a difference between SS, German Silver, and the Aurigan? Mikmar also has one in a copper alloy they call Cupreon. Everyone insists theirs is best.
The difference can be dramatic, or subtle. My mare went fairly dramatically different in GS. My stallion prefers Neverrust, when it really comes down to it… but there is a subtle but real difference between GS and SS.
The cuve of the arms can be as important as anything. The stallion MUST HAVE CURVES. The first time I tried a Myler on him, even though it was too bit, there was this huge difference. I then found JP bits which are just slightly thicker and yet still curved–and half the price. He went fabulously in a JP fullcheek until we began 2nd/3rd-ish work and the fullcheek was a little too dead. (I’d about sell my soul for a JP Fulmer, but I digress.)
On some horses too, with fine heads, loose rings begin to develop gag action. The way the old “Irish Hunter” bits worked on a TB head–big ol’ 4" rings… well, put a nice big 3" ring on a refined head and muzzle–same effect. It can be just too much.
In the end, the absolute best thing you can do is borrow. Borrow EVERYTHING and see what your horse likes. My first mare was very light and elegant, always just, just behind the contact though. Just enough for there to be real tension in the poll/neck/back etc. The weight of the reins was the extent of her contact, ever. Then one day I tried an HS mullen, and it was nothing short of miraculous. A MULLEN mouth of all things.
Ironically, the stallion’s favorite bit (they are similarly bred on the sire side, FWIW) is a mullen mouth pelham. I’ve never quite found the snaffle he’s AS blissfully happy in… but we’ve come close.
Beg, steal… BORROW… really. Try as many as you can. It’s often counterintuitive. It’s their mouth, let them decide.
