I work at a SMB where our licensing costs for VSphere and Windows Datacenter (which we also license) are roughly the same. We've been running everything on VMWare products since VMWare Server 2 (the app you installed on top of Linux, back in the late 00's). Yes, we're paying for Datacenter to run on top of VSphere. We get really good deals on both of them, that will become untenable if our footprint gets much larger.
The one huge factor influencing the platform we're on is pricing. If we added too many more hosts than what we have now, VMWare would be out of the running purely on cost. Microsoft has their *entire history* working against them, so I don't really know what I can stomach once Dell prices themselves out of the running.