Ask HN: Project Management Software or Google Docs?

I'm working for a startup in the travel industry and I've been thrown into a project management role. I've been using Google Docs to manage the development backlog but it's getting pretty messy. Wondering if anyone has any insight on whether or not moving to something like Rally Software or a different SaaS project management tool would be overkill or a good move for a small dev team (3 coders and 1 designer)?