Avoid using $q unless necessary. Most async methods already return a promise

service.js

/**
 * This service showcases when to use $q to return promises and when it's not necessary'
 */
angular.module('sample').factory('sampleService', ['$q', '$http', function ($q, $http) {
  var service = {};

  // Use constants, don't do this
  var url = 'https://api.github.com/users/pablotdl/repos';

  /**
   * This service uses $q to wrap an $http call to the Github API
   */
  service.getRepos = function () {
    var deferred = $q.defer();
    $http.get(url)
      .success(function (data) {
        // Assuming $http will deserialize the JSON response automagically
        deferred.resolve(data);
      })
      .error(function (error) {
        deferred.reject(error)
      });
    return deferred.promise;
  }

  /**
   * This service returns the promise returned by $http directly
   */
  service.getReposProper = function () {
    // Unlike then, success callbacks cannot be chained
    // Then callbacks will be executed one after the other.
    return $http.get(url)
      //The then callback will receive a response... we are only interested in the data property
      .then(_.property('data'));
  }

  /**
   * In this example, we want to return the URL we are using, but want to do so maintaining
   * the promise pattern
   */
  service.getUrl = function () {
    var deferred = $q.defer();
    deferred.resolve(url);
    return deferred.promise;
  }

  /**
   * And this is how it should be done
   */
  service.getUrlProper = function () {
    return $q.when(url);
  }

  return service;
}]);