I've been using JBoss Application Server professionally since 2002. During this period, I've also used Tomcat, Jetty, Glassfish, IBM WebSphere and the already dead OC4J. Between these options I would say my personal choice always was JBoss. Do not misunderstand me; Tomcat and Jetty are both great and lightweight web containers. But the point of this post is not to discussion anyone's preferences, but my experiences with the new version of JBoss Application Server (AS).