As you’d expect, the correct answer to this questions is not between which one to use, but rather which one you need. And the best person to answer this is the developer himself.

• angular.copy(source, destination) : Here we create a full or deep copy of the object. Essentially a new copy of the object is made, there are now two object pointing to two different memory locations which have the same identical data.
• angular.extend(destination, src1, src2 …) : Here we create a shallow property copy from one or more source objects to a destination object. The destination will contain all the properties from all the sources.

Check out this code snippet to give you a better idea:

var src = {'id' : '420', 'product' : 'Orange Juice'}
var dest = {}
angular.copy(scr, dest);
console.log(dest);
 
//The output would be: {'id' : '420', 'product' : 'Orange Juice'}

var src1 = {'id' : '420', 'product' : 'Orange Juice'}
var src2 = {'brand' : 'Tropicana'}
var dest = {}
angular.extend(dest, src1,src2)
console.log(dest);

//The output would be: {'id' : '420', 'product' : 'Orange Juice', 'brand':'Tropicana'}

Now based on your usage, you can choose between angular.copy or angular.extend. For further reading, check out angular.copy and angular.extend.