What are the differences beetween Component.query and Controller ref?

Hi all, What are the differences between Component.query and Controller ref?

can i use both or one in my controllers to get a button's properties? for example:

Code:

    refs: [
        {
            ref: 'refMyButtonOne',
            selector: '#btnOne',
            xtype: 'Ext.button.Button'
        },

.
.
.
.
var myBtn=this.getRefMyButtonOne();

and in the same way i can use :

Code:

var myBtn= Ext.ComponentQuery.query('button#btnOne')[0];

so in both cases, i get the button's properties, so what is the best way to get the property of a class inside my controllers? and what are the difference between them?

Thanks a lot.