For the last couple of years I've been working on both Grails and Rails apps.

Grails is great when comparing it to what came before it in Java land, however, given the choice on a greenfield project, especially one I'm doing for fun, my gut instinct is to reach for Rails. One reason being Rails has noticeably quicker startup times and has less need to restart the app during development. To be clear, Grails startup time isn't terrible, but Rails is faster, and you notice it when you're working with both.

I am open to new technologies and learning new things but there is nothing I hate and despise more than anything with the word "java" in it.