This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
Just search this forum - there's plenty of discussions about this. Take them all with a pinch of salt where the say "A is better than B" without giving a reason (but I'm sure you'd do that anyway). People have listed plently of features they like so maybe you can get an idea.