Final answer:
The ulnar collateral ligament is the best support for the medial side of the wrist, connecting the medial epicondyle of the humerus to the medial ulna.
Step-by-step explanation:
The ligament that provides the best medial support to the wrist is the ulnar collateral ligament. The ulnar collateral ligament is an intrinsic ligament located on the medial side of the elbow joint; it connects the medial epicondyle of the humerus to the medial ulna. This ligament plays a crucial role in stabilizing the medial aspect of the wrist. In contrast, the radial collateral ligament is involved in supporting the lateral side of the elbow, and the transverse carpal ligament is related to the carpal tunnel, affecting the median nerve but not primarily functioning as a medial stabilizer of the wrist.