Certainly the most flexible VDI solution I've worked with, Citrix XenDesktop is the model of compatibility coupled with excellent capabilities. XenDesktop not only works with Citrix XenServer, but also runs on top of other vendors' hypervisors.
An excellent platform for building an enterprise VDI solution, VMware View 5 takes advantage of all the features, services, and fault tolerance built into VMware's flagship vSphere hypervisor.
Back in the old days, the only realistic way to connect multiple remote sites was by T1 or T3 delivered either point-to-point or via Frame Relay. These were either slow and expensive or fast and unbelievably expensive. Then came MPLS, which dispensed with the need for point-to-point circuits from site to site, but was still bound by high expense. You got what you paid for. These circuits were not only reliable, but if a T1 or T3 circuit dropped, you could generally count on the carrier to jump on the problem quickly and resolve it with some expediency.
For more than two decades, I've been involved in designing wide area networks to allow the various office locations within large companies to communicate with one another. I thought I'd seen everything. Then one day my company's CFO came to me with a troubling request. He asked me to reduce our voice and data networking costs by 40 percent.