which is the best CI_authentication module ?

[eluser]Mark Croxton[/eluser]
There was an interesting discussion about this on Stack Overflow:
http://stackoverflow.com/questions/34698...ry-is-best

Tank Auth was written in response to Jens Roland's post and pretty much implements his best practice recommendations.

It's bare bones compared to DX Auth (no profile management, no roles, no access permissions) but you can add these yourself and tailor them to your application's specific requirements. This is a good thing IMHO.