Ask HN: Stay with Java or learn something new for Web Applications?

I have an idea for a web application which I wanted to code as a side-project for some time. I already have experience with Java and C# because I learned them mostly during University and Internships.

What would you recommend? Stay with Java and try to get better with it? Or learn something new? There are too much possible choices and I have a hard time deciding what too use.

I was quite excited when I found dropwizard though.