Free = ESXi = HyperV
Managed = not free = vSphere = Virtual Machine Manager
Microsoft's Virtual Machine Manager is not free and has other component requirements that will significantly add to your implementation costs unless you are already running Systems Center and SQL.
The last time we tried HV & VMM was Windows 2008 R2 w/ VMM 2010. MS brought in a partner to set it up as a direct comparison to our production vSphere plant. It was a joke.
I think we had to stand up 2 or 3 extra servers (VMs) to manage VMM and it's guests. Performance was horrible for no reason. VMs would forget which disk to boot from. NIC bonding was still unsupported (it is now in 2K12). Administration was unnecessarily complex. At a minimum you need to already be a MS shop that is running Windows clustering, SQL, and SCCM.... which we are.
MS says HV 2K12 is so much better. I"m sure we will take a look at it soon enough but I would be suspicious.