Which lens has more power : a thick lens or a thin lens ?

When comparison is done between a thick lens and a thin lens then, a thick lens has more power than a thin lens.

A thick lens (i.e. a lens having surfaces of more curvature) is of short focal length and it deviates the rays more, while a thin lens (i.e. a lens having surfaces of less curvature) is of large focal length and deviates the rays less as power of a lens is reciprocal of its focal length.