Assuming you'd have an online shop, you'd package it in a WAR if it only contains static resources (html, css, javascript) and servlets/jsps/java classes, so standard java web components.
You'd package it into an EAR if you want to add Java EE capabilities such as EJBs (message-driven, session or container-managed beans), enterprise messaging or combine multiple .wars and .jars into one application archieve.
Typically the disctinction is that if you want EJBs, you go with EARs, otherwise go with WARs.