Definitely go for Mercurial and use Bitbucket. It's a DVCS like Git, but with an interface that is (by design) almost as simple as subversion.
Subversion really isn't worth it, IMO, at this point.
I use Git for everything these days because of Github - simply easier to standardize on one VCS, rather than maintaining separate VCS for public and private code (which is where Bitbucket shines -> free private repos). But Mercurial was my gateway to DVCS's back when, and IMO it is really not all that much more complicated to explain and use than SVN, as long as you don't insist on doing overly complicated stuff. If you think your people can handle SVN, then they should be able to handle Mercurial as well.
That being said, we've recently started moving the researchers at my place of work over to Github, and that has actually gone pretty well. Git isn't that hard to use, if you stick to a simple workflow, and Github has pretty excellent documentation.