It is simple, use EAR if you want to use EJBs, use WAR if you don't. Read about the difference between EJBs and POJOs here.

I use WAR during development for it allows hotswap of most of components. When everything is ready i'm going to move to EAR to convert action beans into EJB session beans (i hope this will increase performence).

If you write small app and you do not care about extra services from EJB container then use WAR for it is easier (you may run in class loading issues and other delicate issues with EAR).