I think you are asking a strange question. tomcat  is a web server  engine, but Weblogic and Websphere are both enterprise server.

It is comparing apples vs oranges in this case.

The enterprise server is much more than a simple web server.

Let’s go back to the question  you asked. I think you will find out you are perfectly safe within tomcat. Because Spring framework  is good without EJB. In other word, Spring takes care of all the EJB work for you so you don’t have to use the EJB container.

So if you simply want a server that will serve to the web. Tomcat is your right tool.

If you do want to go fancy, I will recommend you to start trying Glassfish server. Glassfish server is an enterprise server yet it is open source. Even though Oracle bought Sun, this project has not gone under yet. If you do not like the name of Oracle, you still have another open source enterprise server called JBoss.