that must be an old article.
silverstream is almost dying, even thought it's bought by novell (?)
in north america, weblogic is still the most popular, websphere is 2nd i think. oracle is pushing for its app server of course.
a lot of medium-size (more open-minded) companies are using tomcat, jboss now.
It is not just about which AS to pick. It also depends on other context of your project.
If money is not an issue, choose all products of the same company, if possible. Easy configuration and good services.
Personally, I think Oracle AS is more promising than WebLogic. JBoss is an open-source AS. But the documentation is rather crap.
If you develop and test at home, Oracle AS requires less memory than Websphere and WebLogic and faster than them.