From what I understand they are all pretty much the same. The major differences are their complexities. Providers are configurable at runtime, factories are a little more robust, and services are the simplest form.

Check out this question AngularJS: Service vs provider vs factory

Also this gist may be helpful in understanding the subtle differences.

Source: https://groups.google.com/forum/#!topic/angular/hVrkvaHGOfc

jsFiddle: http://jsfiddle.net/pkozlowski_opensource/PxdSP/14/

author: Pawel Kozlowski

var myApp = angular.module('myApp', []);



//service style, probably the simplest one

myApp.service('helloWorldFromService', function() {

    this.sayHello = function() {

        return Hello, World!;

    };

});



//factory style, more involved but more sophisticated

myApp.factory('helloWorldFromFactory', function() {

    return {

        sayHello: function() {

            return Hello, World!;

        }

    };

});



//provider style, full blown, configurable version     

myApp.provider('helloWorld', function() {

    // In the provider function, you cannot inject any

    // service or factory. This can only be done at the

    // $get method.



    this.name = 'Default';



    this.$get = function() {

        var name = this.name;

        return {

            sayHello: function() {

                return Hello,  + name + !;

            }

        };

    };



    this.setName = function(name) {

        this.name = name;

    };

});



//hey, we can configure a provider!            

myApp.config(function(helloWorldProvider){

    helloWorldProvider.setName('World');

});





function MyCtrl($scope, helloWorld, helloWorldFromFactory, helloWorldFromService) {



    $scope.hellos = [

        helloWorld.sayHello(),

        helloWorldFromFactory.sayHello(),

        helloWorldFromService.sayHello()];

}​