[fChk]

i have searched on google as well and had asked in freevps.us aswell i think but there were different views some of them told me that OpenVz does not use lot of memories and some told me that i should use KVM.
I was just confused till now then why people prefers KVM if OPENVZ uses less resources

The short answer is because those people are VM "consumers" not "producers"; hence they are more concerned with getting a real VM that they can tweak, customize and secure as it is possible. KVM virtualization offers that possiblity while OpenVZ can't. I learned this the hard way, the last time I had a VPS @Gigarocket (3/4 years ago.)

In contrast, It's the guys selling those VMs who care much about the resources that each virtualization technology need for a smooth service. Although, it's no secret that they generally prefer using OpenVZ virtualization because of the overselling aspect of it (meaning MORE PROFIT.)

Now for some theory about these 2 kind of virtualization technology, although @Hidden Refuge mentioned this already, but I want to stress on the container aspect of OpenVZ (as I worked a lot with Docker containers which is another application oriented container tech of 2013.)

I will start with KVM (Kernel-based Virtual Machine), which is generally considered as a type II hypervisor (some/RedHat consider it type I, i.e. bare metal), responsible for the "classic" hardware virtualization that allows you to run multiple, completely isolated VMs.

In contrast, OpenVZ is an OS-level virtualization software that relies on a patched version of the Linux kernel to split the physical server allowing you to run multiple isolated containers. Yes! Your VPS is just a container in this case. This is why it's lightweight resources-wise and this why resellers can oversell its VMs.

In short, OpenVZ is a "system container" platform designed to host complete guest OSes without requiring any emulation (relying only on Linux kernel advanced features in process management, security etc....)