Final answer:
The median cubital vein is the preferred site for routine venipuncture because of its size, superficial location, and stability during needle insertion.
Step-by-step explanation:
For routine venipuncture, the median cubital vein is the most commonly used vein. This vein is located in the antecubital fossa, also known as the front of the elbow, and is a branch that arises from the basilic vein and crosses over to join the cephalic vein. The median cubital vein is preferred for several reasons, including its relatively large size, superficial location, and the fact that it does not tend to move around when the needle is inserted, making it a safer and more comfortable choice for patients. In contrast, the radial and ulnar veins are less commonly used due to their deeper location and tendency to move, which can increase the risk of complications.