Eric Van Essen did a presentation at last year's SolidWorks World that outlined some of the differences between EPDM and PDMWorkgroup. I've uploaded it for you to take a look.
One thing you need to think about is how you plan on using a PDM - what are your expectations?
Check out Van Essen's presentation as a starting point.
20651 - Van Essen.pptx 4.6 MB
Thank you Adam, that is just what I was looking for.