If you're looking at a single, stand alone hypervisor, then the differences are not enormous. You could pick your flavor based on whatever you're comfortable wi

If you're looking at a single, stand alone hypervisor, then the differences are not enormous. You could pick your flavor based on whatever you're comfortable with. When you're looking at larger scale and the potential for unique and/or fringe cases goes up, then support for those becomes a differentiator. VMware rather excels here I think, with support for device pass-through and higher resource limits. GPU acceleration, Raw Device Mapping, are some of the ones I can think of. A little past that and it's interaction between hypervisors. ESXi and KVM will do live migration, but KVM doesn't have DRS (yet). I don't think Hyper-V has storage live migration yet, but ESXi does. And so on. They'll all catch up, I've no doubt. I'm particularly interested to see Nutanix with their Acropolis/KVM hypervisor gain these features. But right now, ESXi is in the lead.