I ride my barrel horse in a medium ported curb bit with a copper roller. The shanks I think are 5 or 6 inches. If I put any kind of jointed bit in his mouth he gets very uptight. He responds to one fine, but he is so much more relaxed in the curb bit. My pony that I take to local shows every now and then to do barrels on for fun rides in just a halter. He just doesn't like any kind of bit in his mouth and works a lot better in just a plain ole rope halter.
I tried Nico in everything. He would go well in anything with poll pressure. We did well with a regular curb but he didn't turn as well. We graduated him to a jr cowhorse bit with a copper mouth piece. It worked really well.
I have used wonder bits, short shanked hackemores, short loose shanked curbs, etc...Also used regular snaffles...from O ring to full cheeks, and single and double jointed mouthpeices.
My current mare goes in a D-Ring, or in a rope halter...I am hoping to take her to her first show mid Sept. I am not expecting to win, or anything, it's just going to be more for the experience for her, and through the winter we will continue working on getting more soft through the bridle, and then adding more speed.
Tanner rides in a snaffle (anything more than that and she gets upset), and Magic rides in either a TT or a snaffle, depending on how headstrong she's being that day. I've considered trying Magic in a Jr. Cowhorse, but haven't really been able to lay my hands on one yet.
I've used a little of everything.
Snaffles (o-ring with and without twist)
Loomis (typically what I ride in day to day)
I like bits with a good bit of gag on them, but have used more fixed mouth peices as well.
Jr Cow horse w/ a slight twist.
I've got a few L&W lifters. One chain mouth peice, one dog bone, and one squared off.
Sixes and I really like one of my newer ones. It's a ring bit with a little curb action.
And, I think my last in the group would be a curb with a full slide on it.
I really like a bit with a good bit of gag to it. It allows the horse to think before reacting. I want them to do what I ask when I ask it, but I don't want them to be afraid of contact with the bridle. I want nice smooth transitions...not jerky movements.