The Latest Version CI 2.1.3

Developing Web Applications in PHP and AJAX 

The Latest version of Codeigniter is 2.1.3 version.
bringing some additional security and enhancements to the 2.x stable version. In particular, CodeIgniter 2.1.3 improves IP address resolution in the Input class, preventing spoofing that was possible under certain circumstances.

from : codeigniter.org

The Best Framework PHP

The Best Top 10 Ranking Framework PHP.

1. Yii (http://yiiframework.com)
2. PhpOpenBiz (http://www.phpopenbiz.org/jim/)
3. CodeIgniter (http://www.codeigniter.com/)
4. CakePHP (http://www.cakephp.org)
5. PHPDevShell (http://www.phpdevshell.org/)
6. Symfony (http://www.symfony-project.com/)
7. Prado (http://www.pradosoft.com/)
8. Zend (http://framework.zend.com/)
9. Akelos (http://www.akelos.org/)
10. eZ Components (http://www.ez.no/ezcomponents)

Source: http://www.phpframeworks.com/php-frameworks/index.php?id=8