The main difference between red and green enchilada sauce is the types of chilis used to make them.  Red enchilada sauce is generally made with red chilis, along with various spices and seasoning.  Green enchilada sauce, on the other hand, is made with a base of green chilis, along with tomatillos and other spices.   One is not automatically more spicy than the other - both red and green enchilada sauce come in a range of spiciness from very mild to super spicy.