I'd say mercurial will be easier to deploy across that range of systems, and easier for people not familiar with the command line (Dreamweaver users ;)) to use.

I'd say mercurial will be easier to deploy across that range of systems, and easier for people not familiar with the command line (Dreamweaver users ;)) to use. Personally, I feel that git is technically superior, but throwing Windows into the mix changes things up a bit. You can use git confidently in Windows - I do at home, using Cygwin - but in terms of graphical support, it's still reasonably dodgy. You could definitely look into TortoiseGit, and then configure it using mSysGit and putty (I've tried this in the past and it works well) - but if anyone then wants to use Cygwin, things get very complex. GitX is good for Mac users though!