It's really hard to choose just one favorite feature. I love the random plant photos--I get to see plants I've never seen before. I love the articles and tips because I always learn something. It's such fun to show our "badges" that express our interests.
The wealth of knowledge here is amazing, from the plant database to the forums, and the social aspect here is most enjoyable.
Perhaps I'm a bit indecisive
but there aren't any features of ATP that aren't special to me.
One thing that drew me in to the original DG was how safe and secure the site was...no spam, pop-ups, etc. I love that Dave and Trish have made such a secure site for us to share all of this wonderful information and chat with friends.