The difference between angular service, factory and provider when declaring as an injectable argument.

Services

module.service( 'serviceName', function );

When declaring serviceName as an injectable argument you will get a reference to the actual function passed to module.service(…).

Factories

module.factory( 'factoryName', function );

When declaring factoryName as an injectable argument you will get the value that is returned by invoking the function reference passed to module.factory(…).

Providers

module.provider( 'providerName', function );

When declaring providerName as an injectable argument you will get the value that is returned by invoking the $get method of the function reference passed to module.provider(…).

Sample code

HTML:

<div ng-controller="MyCtrl">
  <p>{{service}}</p>
  <p>{{provider}}</p>
  <p>{{factory}}</p>
</div>

Javascript:

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

var func = function() {
    this.name = "func name";
  this.$get = function() {
    this.name = "func $get name";
    return "func.$get(): " + this.name;
  }
  return "func return value: " + this.name;
}

myApp.service('testService', func);
myApp.provider('testProvider', func);
myApp.factory('testFactory', func);

function MyCtrl($scope, testService, testProvider, testFactory) {
    $scope.service = "the Service is actual function value = " + testService;
    $scope.provider = "the Provider is actual function value = " + testProvider;
    $scope.factory = "the factory is actual function value = " + testFactory;
}

The sample code also can be found on JSFiddle.