If you deploy a virtual infrastructure from scratch, you must weigh function against price to determine which hypervisor vendor best fits your needs. To make an informed decision, you need to know what types of workloads you will deploy, which operating system you will use, how VM applications are licensed and any associated management costs.
If you plan to run several Linux VMs, usually VMware and XenServer give the best functionality and breadth of support. For Windows workloads, you may get better overall licensing with Hyper-V and Windows Server Datacenter Edition on the host. All your Windows Server VM licensing would be free with unlimited virtualization rights inherent in the Datacenter Edition, without any further cost for the hypervisor. To implement a larger VDI environment, XenServer paired with XenDesktop offers the best function and value.
Bottom line: Comparing functionality with price is a difficult and individual process for every organization. Take time to look past the marketing and become an expert on every licensing facet.