That’s a tough one! I guess the most effective adaptation would be something that does what it needs to do really well. A mantis shrimp has a hammer like claw that hits its prey so hard that if a humans had a tenth of the strength, we could throw a baseball into orbit!!
All animals are well-adapted in the sense that they are the surviving descendants of the very first animals and to have survived to the present day they must have been well adapted. However, humans are rapidly changing the habitats in which many species live, and so those animals are often not so well adapted to the changed conditions. A good example is when tropical forests are chopped down, the forest animals are not well adapted to living in the new farmland or cities, and so they die out.