suggestions about Authentication with CI

[eluser]Alejus[/eluser]
Hi everybody.
I need your opinion and suggestions about the best library for use in authentication and manage of users and levels.

I´m developing a system and I was looking for some library about it, but.. I´dont know which is the most used or the better for you.

And if is posible, some example for to implement in my app.

Thanks for the time to answer.

Alejus.
From Argentine.