Anyone who as asked that question before will remember that the bit I always use and advocate is one with a Billy Allen mouth piece. It allows one shank to swivel without effecting the other shank. In turn, each shank can swivel outward. The barrel in the center only allows a small amount of movement (the misnomer of a nutcracker). The bit I use has calvary style shanks that sweep back minimizing the length.
Personally, I only use two bits, either a single joined snaffle or this bit: