A cactus plant of your choice. Buy a healthy plant of average size. Very small plants may sometimes take years to grow to a standard size.Most of the cactus plants love sunlight, especially those with spines.They should be placed in direct sunlight.Others, which do not prefer sunlight, should be kept in shade.Make it a point to check the plant for any unhealthy symptoms, like drooping or change of color.The problem can be over watering or deficiency of sunlight.
Fix the problem and see the difference.