Polar bears or Tasmanian Devils?

This clearly depends on the aim of your investigation. If you're studying adaptations, go for the polar bear, if you're trying to study the risk of extinction, try the devils have a pretty interesting story. If you're just studying unique mammals, choose the devils. Personally I'd investigate a domestic cat and their ability to land on all fours. Good luck on your project. Provide more details if you want a better answer.