Microsoft responded to the findings by highlighting customers that it says are using its product. “Our customers have their own scorecards, and Ingersoll Rand, Jackson Energy Authority, and the University of Miami have experienced success and cost savings through using our products,” the company said via email.

Burton Group found at least one "preferred" feature that both XenServer and Hyper-V have, but which VMware lacks: virtual storage disk compatibility. "VMware is proprietary; it doesn't support other hypervisors," Wolf said.

Burton Group presented its findings at a session entitled "Hypervisor Competitive Differences: What the Vendors Aren’t Telling You."

It's hard for customers to compare vendors' products using their data sheets because each tries to make its products look best, and sometimes the vendors say they have a certain feature even if it is poorly implemented, Jones said.

Even Glemmestad, an IT engineer with Norwegian agricultural supplier Felleskjopet, said Burton Group's assessment made sense to him. He'd read that the analyst firm considers XenServer production-ready but came to the session to find out on what basis.