GitHub is very polished and they add useful features like pull requests, issue tracking, code comparison view, etc. often.
They are very well setup for "social", open source coding projects. It's easy to fork someone's repo, add a fix then issue a pull request to them.
I would go with git because git is what the cool kids use. At least, this is why I chose it. Herding mentality generally isn't a good reason, but herding works in figuring out who you want to work with.