I'd say it depends - for most cases I'd suggest KVM as you have full OS with kernel so:
you may have best fitting version for guest OS
any custom module or patch without asking provider,
ability to go beyond Linux (e.g. BSD, Windows)
better isolation/security - of course hypervisors might also contain bugs but with shared kernel any serous kernel bug is enough to break isolatio
Also there are more benefits: no problem with systems that require low level access (like Docker, which require special OVZ settings, and works out of the box on KVM), more guarantees on resources, access to VNC console (not only the text one) etc.
On the other hand OpenVZ have less overhead as it's container running only user-land part so it might be bettor for really low specs VPS (like below 512 MB of RAM). But I'll stick with full virtualization - especially if you need new OS version as guest. I've no expierience with OpenVZ/Virtuozzo 7, legacy OpenVZ - but for container part most of the above would be still correct (except for newer kernel version).
OpenVZ is a lighter system and a cheaper option for those who do not have a lot of requirements. In my opinion is one less than the KVM system that is more complete and can run your own kernel having their dedicated resources isolated from other VMs. Unlike the OpenVZ sharing server resources dedicated to other VMs.
I agree with the guys on this, it depends on what you want to do...
Believe it or not, it seems most people seem to like KVM because the resources seem to be more dedicated to them and because it seems to have better isolation.
While many don't prefer OpenVZ, I use it alot for the following reason:
Boot time is much faster since it seems that OpenVZ shares part of the host (I think it shares the kernel but I'm no expert so don't quote me on this)
OpenVZ packages seem to be a lot cheaper than KVM (for obvious reasons)
I could be wrong but I think there are firewalling challenges that occur with OpenVZ (I'm not sure if this is fixed) but I remember someone saying that iptables can act differently on OpenVZ, maybe one of the guys who run host servers on a daily basis could explain that or clear our heads on if this is true or not.
I also read that its a little safer to run KVM because its a little harder for someone to access your files from the host node. I know its pretty easy for the host node to have a look at your OpenVZ files.
In the last few years, virtualization has become a popular option for many companies to increase their ability and productivity while reducing infrastructure costs. There are multiple virtualization technologies available for companies to run their daily operations. However, it has become essential to consider the options before making a choice.
Virtualization technology allows a single system to run multiple infrastructures simultaneously by installing software called a hypervisor, which creates and executes different virtual machines on a single host PC. As a result, openVZ is easier to set up and maintain properly, while KVM takes much more networking knowledge. In addition, openVZ and its templates are more beginner-friendly.
There are two main types of virtualization technology: KVM and OpenVZ. KVM is an open-source virtualization technology for Linux and a complete solution that allows you to run multiple operating systems on a single server. OpenVZ is a container-based virtualization solution that allows you to run multiple instances of a single operating system on a single server.
OpenVZ is an operating system-level virtualization technology for Linux. It creates multiple, secure and isolated Linux Containers on a single physical server which acts as a stand-alone server. OpenVZ only hosts Linux Operating Systems, while KVM is much more flexible than OpenVZ.
KVM allows its users to allocate values to their resources. Thus, applications only use the resources that are needed. It means companies can perform at a high capacity with lower needs from the hypervisor. At the same time, OpenVZ uses a shared kernel with a virtualization layer on top of the existing Linux OS. Therefore, this kernel is shared by all VPS users on the node, and the kernel is not customizable.
Pros of OpenVZ:
Speed & Scalability
Pros of KVM:
Dedicated Memory Usage
Thus, I hope the above information helps you to choose between KVM or OpenVZ virtualization.