I think entire giant essays have been written about this topic. However, it boils down to a few things. Mercurial tends to choke on large repositories. Git d

I think entire giant essays have been written about this topic. However, it boils down to a few things. Mercurial tends to choke on large repositories. Git doesn't. A lot of people know git. Not many people know mercurial. People like to bitch about git's command-line interface. But most of the quirks have been ironed out over time. What you're left with is a very UNIX-y program. If you understand the concepts then you will figure it out. git also has pretty good Windows support now, thanks to the GitHub client and others. I don't know much about Github versus BitBucket (or any other site.) I use GitHub because we use it at work and because I found it first. BitBucket now supports git repos, which might make it a contender. I get the feeling that you're more likely to get contributors if you start on GitHub, simply because people are more familiar with the site's interface. But nothing I put on Github has become mega-popular at this point, so I don't know.