Comparison of different ways to have private members in Objective C

I came from C++/Java world where it's quite obvious how to create private members. However, I saw several ways to do this in Objective C and I would like to hear cons and pros

1) Declare them as @private in .h file

@interface MyClass : NSObject
{
    @private
    int someMember;  
}
@end

2) Declare them in interface inside .m files

@interface MyClass() {
    int someMember;  
}
@end

@implementation MyClass
@end

3) Declare them in implementation

@implementation MyClass {
     int someMember;  
}
@end 

What is the preferred method and why? Did I miss any other methods?