Try to decide which of the features you mention -- simplicity, flexibility, POCO support -- will be most useful to you and your project(s) one year from now. Which is most likely to make your work easier?
Then you'll have your answer. And if you still can't choose, pick Dapper (just a random selection I made :-) As the Cheshire Cat says, if you don't really know where you want to go, it doesn't matter which road you choose.
