These are two different virtualization machines. VMware is slightly faster than Xen on most operating systems. Still, this gap extends on the Windows platform, where Xen tends to score lower. Xen operates paravirtualization, where it alters the operating system it is running on so that the instructions are directly sent to the hardware.
VMware uses binary translation and emulation and does not necessitate any change of the operating system that it is running on. This change makes VMware easier to install and control compared to Xen. When it comes to the hardware, VMWare is the more preferred choice. This preference is because there are no constraints to using Xen. Xen requires that the hardware utilized with their software is either Intel VT or AMD-V. This necessity means that users with incompatible hardware need to upgrade regardless of how powerful their system is.