What is the difference between KVM and hyper V?

One of the major differences between vSphere and KVM, Hyper-V and XenServer has been the ability to integrate3rd party distributed switches.
Xen, Microsoft Hyper-V, and VMware are all bare metal hypervisors, which means that they are hosted on the computer like software.
They need special boot-time support and none of them employ a full paravirtualization like KVM does.
KVM runs inside your Linux machine as a hosted hypervisor makes it easier to deploy and manage.
However, compared to the other programs, it makes it harder to provide good performance.
If your company runs Linux, BSD, or Solaris operating systems, your best bet may be Xen virtualization.
It comes with some great management software and3rd party apps are available.
For windows and other operating systems, all of the virtualization software is pretty similar when comparing performance and features.

The short answer is use KVM if your have more Linux/Unix servers and Hyper-V if you have many servers running Windows.
And believe me if you have mixed environment and you have to select one hypervisor VMWare is best.