So I am writing this before I have tested to actually see if it pans out. But from what I can tell Hyper-V maybe the better choice for VDI. The reason I am saying this is the way it handles memory over commitment. The way both XenServer and VMWare handle memory over commitment is they will wait until the Host is running low on Physical Memory then it will start telling the VM's to hand their memory back, causing lots of thrashing and over loading the Kernel of the Host. Now the way Hyper-V handles this is just a little different. It starts VM's actually using the minimum set value of RAM vs. XenServer and VMWare where it starts VM's using the Maximum and then the host slowly reclaims memory. Hyper-V is better for VDI in this way as it starts the VM's using the minimum allocated RAM it stacks easier and makes less over head on the Kernel for as it doesn't have to keep requesting Physical Memory back.
So conclusion is for VDI Hyper-V has the potential to be a great foundation however it is still pretty new to the enterprise space as well as XenServer. I hopefully will be able to get some time to actually test this in the next few weeks but definitely wanted to get it out there as food for thought.
Thanks for reading