Question

I wonder when I should use Core Data and when I just should keep it easy and use delegate variables?

Answer 1

Delegate is a design pattern, CoreData a persistence framework. You are comparing things, that are not compare-able.

Edit

Delegate:

A delegate is an “entry point” where an objects allows you to define some custom action.
It is similair to callbacks in some language or interface in Java.
Technically a delegate is just a pointer to an object that conforms to a defined protocol

Delegation is a simple and powerful
pattern in which one object in a
program acts on behalf of, or in
coordination with, another object. The
delegating object keeps a reference to
the other object—the delegate—and at
the appropriate time sends a message
to it. The message informs the
delegate of an event that the
delegating object is about to handle
or has just handled. The delegate may
respond to the message by updating the
appearance or state of itself or other
objects in the application, and in
some cases it can return a value that
affects how an impending event is
handled. The main value of delegation
is that it allows you to easily
customize the behavior of several
objects in one central object.

CoreData

CoreData is a Framework for organizing persistence data.

In simplest terms, Core Data is an
object graph that can be persisted to
Disk. […] Core Data can do a lot
more for us. It serves as the entire
model layer for us. It is not just the
persistence on disk, but it is also
all the objects in memory that we
normally consider to be data objects.

—Marcus Zarra, Core Data