According to an article in the FITNESS AND SPORTS REVIEW INTERNATIONAL, the reverse trunk twist is the most effective exercise to target the abdominal oblique muscles. In this exercise the spine remains in basically its normal anatomical position to allow for rotation through the full range of motion. In addition, there is little to no chance of injury to the spinal discs or spine.
In contrast, when using the sit-up with a twist the rotation is done with a bent spine, which creates great shearing forces on the discs. This can cause injury. In addition, in the sit-up with a twist as well as in the lying shoulder rotation exercise, the range of motion is minimal.