It might depend on the typical hardness of the ground that they are used in. If you have soft soil, then just about any skinny stake will push in. If you have really hard soil, it won't push, and you may have to pound it in using a rock. In that case, you probably want the stiffer one with larger diameter.
On the other hand, with hard soil, maybe a small number of stiff ones will get the job done. With soft soil, maybe you need a larger number of the skinny ones.