I would like to add authentication to my Rails app. I came across few plugins that do this: acts_as_authenticated, restful_authentication, Authlogic...etc
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I personally tend to use restful_authentication out of habit, but I've made use of AuthLogic a few times. AuthLogic is a lot leaner and cleaner code and tends to be much easier to setup and integrate into a project. It is also is newer and more popular (or feels like it as of late), so it should be easier to find resources or help if you need it. I'd definitely go AuthLogic.
If you'd like to know more about restful_authentication and see how it varies from AuthLogic in practice, there is also a railscast for it.
http://railscasts.com/episodes/67-restful-authentication