Of course the answer will always be "it depends on your requirements". If you work for IBM the choice will likely be WebSphere. All others should choose Weblogic. :-) :-)
I've co-architected and developed a production project using Weblogic and one using WebSphere. There is simply no comparison in the level J2EE support and reliability between these two products IMHO (especially if your project will use EJBs). As a consultant, I can not recommend WebSphere unless the project relies only on JSP, servlets and JDBC. One day the WebSphere product will mature -- that day has not arrived. Weblogic has been ready for high-quality J2EE production systems for atleast two years and shows no signs slowing down (literally).
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