The major difference between convert.ToString() and ToString() is that,

convert.ToString() handles null but ToString() does not handles null.

Please see below two set of code:

This code will run successfully, no exception will be raised for that:

    string name = null;

    string abc = Convert.ToString(name);

Below code will give an exception, unhandled Exception:NullReferenceException

    string name = null;

    string abc = name.ToString();