What's the preferred way to instantiate one class in another?

Pretty basic question. Has to do with design preference but I think there are some caveats that I'm missing.

I want to have an instance of some class inside another class. The way I see it, I have 3 options:

1. Have the object class2 inside class1 as I have it below. This means it gets constructed when an instance of class1 gets constructed. My issue here is that it may need a default and/or copy constructor? When I instantiate a class1 object below, does it construct class2_inst(args) using that constructor? Or is class2_inst already created with some default constructor and the line class2_inst(args) simply copies an anonymous class2 object?

   class class2 {
     public class2(args) {
       ...
     }
   }
   
   class class1 {
     protected class2 class2_inst;
     public class1(args) : class2_inst(args) {
       ...
     }
   }
   

2. I can have a pointer to class2:

   class class2 {
     public class2(args) {
       ...
     }
   }
   
   class class1 {
      protected class2* class2_inst;
      public class1(args) {
       class2_inst = new class2(args);
       ...
      }
   }
   

   This has the advantage that class2 isn't instantiated until I explicitly call the new operator.

3. Then there's using a reference instead of a pointer:

   class class2 {
     public class2(args) {
       ...
     }
   }
   
   class class1 {
     protected class2& class2_inst;
     public class1(args) {
       class2_inst = new class2(args);
       ...
     }
   }
   

I want class2_inst's life-time to match that of class1. No funny business with having class2_inst living outside of class1. So references may be the way to go.

Of the 3 methods, which is everyone's preferred way, and why?