Even those who don’t practice religions such as Buddhism, Hinduism, or Sikhism definitely consider the pros and cons of reincarnation. While a new life and body sounds amazing after you die, rebirth loses its charm when you consider coming back as one of the worst animal reincarnations. No one knows what happens after you die, but everyone most certainly knows they don't want to come back as animals with hard lives. Should you fail to come back as a beautiful animal, the circle of life becomes a wheel of torture. Obviously the earth needs dung beetles, but does it really need you to be one? As cool as an exoskeleton sounds, it pales in comparison to having thumbs and warm blood.
With that in mind, you must consider the animals you wouldn't want to be reincarnated as. Factors such as habitat, diet, and of course, looks must come into consideration; who cares that you're a mammal when your proboscis defines everything about you. If you manifest hard enough and live a decent life, you can hopefully avoid coming back as a farm chicken or tapeworm and instead be a golden retriever or a dolphin. Ideally you come back as a human and get a chance at round two, but if you return as a tongue louse, it'll give you time to reflect on how you got there in the first place.