1、Global Events
Code:
Ext.fireEvent('userchanged');

//listen in controller
listen: {
    global: {
        userchanged: 'onUserChanged'
    }
}
2、Controller Events / Application Events
Code:
MyApp.app.fireEvent('userchanged'); // or Ext.app.Application.instance.fireEvent('userchanged')

//listen in controller
listen: {
    controller: {
        '*': {
            userchanged: 'onUserChanged'
        }
    }
}
I wonder which one is better