Well, it depends on what you want to do. Class now supports setup and init methods that happens when a class is created. Setup is used for classes where you 99% of the time want the standard initialization routine to run. Init is for all the other situations. Controller is the best example of this.
In 2.0's controller's we always had to do:
init : function(el, options){
this._super(el, options)
// custom initialization function here
}
I would even forget to call _super. And, if the creator of the library is having problems, there's a problem.
So, I made it possible for classes to have 2 setup type functions. Model uses the same pattern (doing most of it's work in setup), so that you don't have to call this._super to get your model setup correctly.
You should still be able to use init, it's just model's setup code will have already run.