Difference between transform.localEulerAngles and transform.localRotation=Quanerion.Euler

I am working on a project which I have inherited, and I’m confused by the way in which two similar objects are being rotated but using different methods. There is a parent object with multiple daisy-chained children (a robot arm style link chain).

One has a script applied to each child joint and uses localEulerAngles:

 transform.localEulerAngles = new Vector3(0.0f, setAngle, 0.0f);

The other has a script applied to the parent which references the children in the inspector, and uses localRotation = Quanterion.Euler:

 public GameObject objectToRotate;
 float setAngle;
 private Vector3 axis= new Vector3(0, 0, 1);
 objectToRotate.transform.localRotation = Quaternion.Euler(axis*setAngle);

What is the difference between these approaches when one uses Euler angles directly and one uses Quaterions?

Thankyou.