Oracle GlassFish Server 3.0.1 Application Development Guide

How to Choose the Type of Connection

If you anticipate that your web application will need to send frequent updates to the client, you should use the HTTP-streaming connection so that the client does not have to frequently reestablish a connection. If you anticipate less frequent updates, you should use the long-polling connection so that the web server does not need to keep a connection open when no updates are occurring. One caveat to using the HTTP-streaming connection is that if you are streaming through a proxy, the proxy can buffer the response from the server. So, be sure to test your application if you plan to use HTTP-streaming behind a proxy.