I started this project based on appfuse but a framework like Grails is maybe more appropriate. Since I'm in the very beginning of the project I'll probably should do the switch now.

The nice thing about groovy is that it will be easy to refactor to java if needed.

The nice thing about grails is that it's based on the JEE stack.

The only argument I find against moving to grails would be scalability but it's way to early to talk about this kind of optimization, according to the rule 'Premature optimization is the root of all evil' .