Much better picture of you guys now :]
As Luvstoride said - Get his teeth checked first.
From what i've read, I would really stay away from any twisted wire mouthpieces and shanked bits.
If you do need to really haul his head in any given direction to ensure he moves for hsi own safety, I would definately stick with a snaffle, as the direct contact is going to be much clearer and more effective in showing him what you want. Direct reining in shanks is not supposed to happen - It can be done, but generally only on horses who understand direct reining in a snaffle first and don't fight it.
To help with your direct reining issues, I would suggest either D ring cheeks, a Tom Thumb snaffle, or a Full Cheek/Fulmer snaffle. All of these bits really enforce a direct rein - the opposite side of the cheek almost 'pushes' the face around as well as the pulling action from the rein. Examples:
Tom Thumb Snaffle (Might not be available in the US):
I think a fulmer would be a very good choice for your boy. They are designed to be used with keepers from the top bar across to the cheekpiece which have the added advantage of keeping the bit very still in the mouth which your boy might like.
As for the actual mouthpiece, try a double jointed bit with a lozenge or french link in the middle (NOT a Dr. Bristol - Different angle than a french link). The head tossing may have been a sign of dislike of the single jointed 'nutcracker' action.
Now, if he starts blowing through your requests to stop, you need to do one or both of two things.
First, look at yourself. When asking for a stop you should ask firstly with your breath (Exhaling), weight (Sinking into the saddle), Legs (Sinking your weight down into your heels) - If he ignores this, then you take up the reins. The most important part of a stop is AFTER the horse has stopped - The millisecond he stops, you need to release everything - reins, breath, weight. Horses learn from the release, not the pressure itself. I think if you really focus on releasing after every stop, he will improve. He is still a baby - We have to exagerate things for them to understand :]
Secondly - An emergency stop. Personally, I don't use and don't like the one rein stop so I will leave that to other people to explain. I use more of a 'pulley rein' method. The idea is to have one rein very short and anchor that hand, either on the neck or just by weight, and use the other rein up high and very strongly to come to a sharp stop.