You really need to answer a basic question first. Do you want to use Mercurial or Git. I had to make this decision earlier this year. Mercurial was by far easier to setup and start using. I ultimately chose Git for the following reasons:
- Most OpenSource Projects are moving from SVN to Git
- Git allowed the most flexibility in whatever I wanted to do. (This is the main reason)
- Third-party integration
If your business might need complicated version control processes go with Git. The learning curve is steep but it will be easier to do what you really want at the end of the day. I will qualify what I mean by 'steep'. The difference between teaching someone Mercurial vs. Git, is trying to get a Windows user to learn Linux command lines.
If you want a quick easy to use DVCS in which you think simple branching and versioning is all you will ever need, don't kill yourself with Git, use Mercurial. But keep in mind most people you talk to in Mailing lists, IRC, etc. will have experience with Git not Mercurial.
If you plan on paying for GitHub or BitBucket, I suggest you also look at Kiln. FogCreek has made mercurial even easier.
