From the AngularJS mailing list I got an amazing thread that explains service vs factory vs provider and their injection usage. Compiling the answers:

Services

Syntax: module.service( 'serviceName', function );
Result: When declaring serviceName as an injectable argument you will be provided with an instance of the function. In other wordsnew FunctionYouPassedToService().

Factories

Syntax: module.factory( 'factoryName', function );
Result: When declaring factoryName as an injectable argument you will be provided with the value that is returned by invoking the function reference passed to module.factory.

Providers

Syntax: module.provider( 'providerName', function );
Result: When declaring providerName as an injectable argument you will be provided with(new ProviderFunction()).$get(). The constructor function is instantiated before the $get method is called - ProviderFunction is the function reference passed to module.provider.

Providers have the advantage that they can be configured during the module configuration phase.

See here for the provided code.

Here's a great further explanation by Misko:

provide.value('a', 123);function Controller(a) {  expect(a).toEqual(123);}

In this case the injector simply returns the value as is. But what if you want to compute the value? Then use a factory

provide.factory('b', function(a) {  return a*2;});function Controller(b) {  expect(b).toEqual(246);}

So factory is a function which is responsible for creating the value. Notice that the factory function can ask for other dependencies.

But what if you want to be more OO and have a class called Greeter?

function Greeter(a) {  this.greet = function() {    return 'Hello '+ a;  }}

Then to instantiate you would have to write

provide.factory('greeter', function(a) {  return new Greeter(a);});

Then we could ask for 'greeter' in controller like this

function Controller(greeter) {  expect(greeter instanceof Greeter).toBe(true);  expect(greeter.greet()).toEqual('Hello 123');}

But that is way too wordy. A shorter way to write this would be provider.service('greeter', Greeter);

But what if we wanted to configure the Greeter class before the injection? Then we could write

provide.provider('greeter2', function() {  var salutation = 'Hello';  this.setSalutation = function(s) {    salutation = s;  }  function Greeter(a) {    this.greet = function() {      return salutation +''+ a;    }  }  this.$get = function(a) {    return new Greeter(a);  };});

Then we can do this:

angular.module('abc', []).config(function(greeter2Provider) {  greeter2Provider.setSalutation('Halo');});function Controller(greeter2) {  expect(greeter2.greet()).toEqual('Halo 123');}

As a side note, service, factory, and value are all derived from provider.

provider.service = function(name, Class) {  provider.provide(name, function() {    this.$get = function($injector) {      return $injector.instantiate(Class);    };  });}provider.factory = function(name, factory) {  provider.provide(name, function() {    this.$get = function($injector) {      return $injector.invoke(factory);    };  });}provider.value = function(name, value) {  provider.factory(name, function() {    return value;  });};