Many reports have showed that Citrix XenServer 5.5 scales better and optimizing for Citrix XenApp is done in a second. With VMware it has been, and still are more complex to tuning the guest OS. VMware claims 30% improved performance for Citrix XenApp hosted on vSphere 4. Feedback from customers and the new “Virtual Reality Check – VRC VSI and Clocks Reviewed 1.0.3” states the same.
Searching the web for Best Practices for Citrix XenApp hosted on VMware I discovered some resources I would like to share with you :Virtualizing Citrix XenApp on vSphere, part I Virtualizing Citrix XenApp on vSphere, part II Best Practices XenApp on vSphere