If you're a web shop, IMO, none of the Java web frameworks are ideal for the fast prototyping that most startups need to do on a regular basis. I've hated every Java web framework I've ever worked with and I've used most of the popular ones. Always felt like I was fighting the framework for one reason or another; too verbose, not expressive enough or too tightly structured.
There are some decent platforms for the JVM though.
There are some decent platforms for the JVM though.