While running a bare hypervisor is more complex, it's more efficient and more secure since there are fewer attack vectors and the footprint of the hypervisor is small. ESXi is free and Hyper V is free. The backup solutions can be pricey though.
I have implemented ESXi and as a hypervisor, it is easier than some, if you wanted to go bare metal there are several choices, but they are all more challenging than a GUI. Generally more attack surface as well.
James and Sandeep love their Windows, so I won't fault them, but as Wendell would point out, "CENTOS is free, did I mention free?" Also, you could choose any major distro and add in KVM support, you aren't stuck with CENTOS.
