[eluser]JamieBarton[/eluser]
It depends on your needs.
Ion Auth has pretty much a few good things built in and from the ground up such as groups, and forgot password retrieval processes..
I think Ion Auth is good for anybody who is wanting to protect an area of their site, and those who wish to do that and expand on it.. The library is very flexible and has a good user guide also.
Personally.. If you're new to CI then it might be your best option from a getting going straight point of view, but if you want to learn and develop yourself then making your own would be a good suggestion too.
I've built many CI auth systems over the past years and learnt a lot from them..
All the best