codeigniter seems flexible, fast and secure as well. I just need to find reasons for it to lack for large projects

[eluser]rogierb[/eluser]
You cannot say something is the best, that is totally subjective.

If a junior team member can use and understand a framework within a day, that means it is useable.
Compared to Yii, Zend and Symfony, CI is very well documented and very easy to understand.

All other comparisons are subjective to personal interest and experience. ofcourse you can compare functionality and speed, but you compare an apple and a lemon too.

Go with the framework that feels right for you and your team

For me, that is CI.