VMware vSphere ESXi is by far the most advanced hypervisor in the virtualization market. There are other players in the market, including Citrix, Microsoft, and Red Hat, however, VMware ESXi is the most prominent and the most feature-rich hypervisor. Let us look at how it is better and how it differs from other hypervisors present in the market:
Hyper-V: Microsoft has their own server virtualization platform known as Hyper-V. It is mostly used by Small Medium Business (SMBs) because of lower license costs, but is gaining in market as well. It has features such as live migration, quick migration, and dynamic memory along with some other features. Microsoft Hyper-V is basically free, but as a customer you will have to buy the required Windows Server operating system. Moreover, you can buy Microsoft System Center software suite to manage a Hyper-V environment from a centralized location, but it will cost extra money.
XenServer: Citrix has a virtualization platform named XenServer. XenServer used to be the most often used hypervisor on Linux-based systems, but lost some market segments because of more efficient alternatives such as KVM. XenServer is based on Xen, which is a free hypervisor that is also part of many Linux distributions as well. XenServer offers additional tools for easier infrastructure management (XenCenter). It is recommended that if a company is already using Citrix products, then it should consider XenServer, as they already have the expertise available from this vendor. XenServer is often used along with Citrix XenDesktop in Virtual Desktop Infrastructure (VDI) environments.
KVM: KVM is a Linux-based open source hypervisor. First introduced into the Linux kernel in February 2007, it is now a mature hypervisor and is probably the most widely deployed open source hypervisor. KVM is used in many products, such as Red Hat Enterprise Virtualization (RHEV).
The choice of hypervisor depends on the requirement. If you need a simple virtualization platform, then you can just get a free version of Hyper-V or ESXi. These two are the most popular hypervisor platforms and have really professional support, while also constantly being extended with new features. XenServer also has its advantages for those experienced in the Linux operating system.