Dpends on the circumstances and the animal actually....wildlife I would immediately put it down and call law enforcement. Cat or dog, family pet type (including a chicken) I would look around and knock on doors to try to locate the owner, if no owner could be found and it was serious enough that the animal would die anyway, I would put it down, if not and I could get it in my vehicle without being mauled by a scared hurt animal, I would take it to the nearest vet clinic.
For the record, I have taken a dog to the vet (I did not hit it, the person in front of me did), I have put down a deer that hit my car and a neighbor's horse that was hit by someone in front of my house. So honestly it depends on the circumstances and animal. Wildlife have a much smaller chance of survival usually because just the injuries and interacting with human bring about fatal shock.
