Given: Use WHS or Win7 to facilitate file shares and nightly/daily backups, possible remote access and other needs as they occur.
If that is the problem's set of constraints, then I vote WHS.
My vote is informed by use of WHS 2008 or v1 or whatever they are calling the "original" Windows Home Server. I played with and discarded the WHS 2011 beta because I am in love with drive extender.
Given a wider range of options, I would ask if there are other considerations. For example, are you a competent Linux admin? If you are, then a broader range of products might appeal. If you are a Windows guy, then I say go with WHS and don't look back.
I have nothing more to say about that.