A recent article in the Journal of Science and medicine in Sports has uncovered some interesting data regarding pull ups. It turns out, some pull up techniques put more strain on the shoulder's rotator cuff. Of these, end range of motion, the reverse pull up, the wide grip pull up and the Kipping Pull up seem to be most likely to cause impingement syndrome.
Of the images above, option A seems to be the least stressful towards your rotator cuff. Furthermore, avoiding the end range of motion without a high shoulder elevation would seemingly avoid narrowing the shoulder's subacromial space. Weight assisted front pull ups in this position will soon be investigated to determine if this is the go to way for clinicians, personal trainers and enthusiasts to begin such an exercise.
Interestingly, it is anecdotally reported that reverse pull ups are often reported as the easiest for novices to perform. Yet this position caused the most amount of external rotation on the glenohumeral joint, and quite a lot of irritation to the supraspinatus muscle, often implicated in impingement syndrome.
While this is a small study, it is the first to collect data on ways to avoid injury when performing a pull up.