Automobile engineering is actually said to be derived from Mechanical Engineering. Though mechanical engineering is a very vast field but it doesn't means that it is superior. It actually depends upon your aim and interest. If you have made your mind that you only want to study about Automobiles then go for Automobile Engineering. But if you want to first explore other fields of Mechanical Engineering then go for Mechanical. The benefit of choosing mechanicsl branch is that you can take Automobile Engineering in specialisation later.
Hope it helps!