There are a lot of ways to answer this question, but you need to ask yourself a few:
1- What are your requirements?
2- What is budget?
3- What are your technology plans and how do they link to a potential PDM system
These are just a few of many....but from my experience with both Workgroup and Enterprise systems my preference would be Enterprise.
1- More functionality
2- More flexibility
3- Tighter control, including items that are not CAD items.
But again it depends on your user pool, budget, etc.
I have used a few different PDM solutions and I would recommend Enterprise.
That said - the ONLY way to get a good PDM system is to FULLY understand your requirements and the capabilities of the PDM software. I cannot stress enough about understanding the software - whichever you choose. Get some training then install the software and use it, configure it, re-configure it, test it, test it again, re-configure..... it helps so you must budget plenty of time before defining your final configuration.
Enterprise PDM can be an excellent tool but if it is badly configured then it will be a nightmare - but the same goes for all the other PDM software out there.