Difference between Factory, Service and Providers

$provide.provider, $provide.factory and $provide.service are more or less the same thing in the sense that all of them are blueprints / instructions for creating object instances (those instances are then ready to be injected into collaborators).

$provide.provider is the most spohisticated method of registering blueprints, it allows you to have a complex creation function and configuration options.

$provide.factory is a simplified version of $provide.provider when you don't need to support configuration options but still want to have a more sophisticated creation logic.

$provide.service is for cases where the whole creation logic boils down to invoking a constructor function.

So, depending on the complexity of your construction logic you would choose one of $provide.provider, $provide.factory and $provide.service but in the end what you are going to get is a new instance.

Example

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() {
    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()
    ];
}