1) Scalablity
To start the comparison, we would choose scalability and config maximums as these are the important aspects to look for while choosing the platform for your cloud.
Microsoft Windows 2012 RC’s Hyper-V 3.0 seems to be promising on scalability than VMware vSphere 5.0. The maximum supported clustered nodes increased to 64 with increase in support of running VM’s i.e 4000 VM’s, more logical processors per host and more Physical RAM per host as compared to VMware.
To Look For : Would you be utilizing the platform to that extent ? I mean if you are an SMB you wont require that scale!! or If your infrastructure isn’t going to scale, then this part shouldn’t matter. I have rarely seen a VM having 1 TB memory with a more than 32 processors (that would be a massive VM though!)
2) Storage
Second comes the Storage which is a vital part of your cloud infrastructure
*Note : “NO Shared Storage Migration” = Shared Nothing Live Migration Feature of Windows 2012 i.e without the shared storage, refer Clustering Section for more details
With Windows 2012 Hyper-3.0 a new virtual disk format is introduced that is capable of supporting virtual disk upto 16 TB, this gives a microsoft a lead as current support in the market is around 2 TB. Though 2 TB space is a lot, I would prefer a large disk space, as we tend to get out of space frequently .. thus bigger the better for me!
The second improvement by Microsoft is support for SMB 3.0 File storage, that VMware doesn’t . SMB 3.0 File storage may be compelling to many Smal/Medium businesses, as its a very cost effective way to build your cloud infrastructure, saving $$$ investment in SAN and other storage.
VMware on the other hand has Storage QOS and Storage classification for esay placment for your multi-tier environment, this is something Microsoft needs to improve on.
To look for : Would you require such large VHD’s for your Virtual machine in your infrastructure ?. Do you really require SMB File Storage, NFS performs bit faster than SMB. If your infrastructure isn’t that demanding, SMB file storage would suit you.
Secondly, though new .VHDX format seems to be a plus point for Microsoft, this format isn’t supported by other vendors and might limit your cloud portability from Private to Public and vice versa or on cross platforms.
3) Networking
Network seems to be important so that your service is available and functional. Windows 2012 and vSphere 5 both supporting almost every feature like NIC teaming, vLAN’s, spoofing protection, Virtual Switch. But feature like Distributed switch that works like a centralized switch across your cloud infrastructure, and VM zoning for Security seems to be missing with Microsoft. Microsoft partners have announced 3rd party extension support for Network switch, but you need to wait!
To look for : Though both products offer similar features, Distributed switch is an added advantage for your Cloud infrastructure as it ensures standard configuration of your virtual switch across all the servers in your cluster. This is vital , so that your features like HA and Live migration to function.
4) Memory Management
This is what determines your Density of your Cloud infrastructure and its performance. Though Microsoft tried hard to cope up with VMware memory management techniques
by introducing Dynamic memory, Ballooning and Memory over-commit similar to VMware, VMware offers more!! VMware has the finest memory management techniques that ensures performance even under heavy workload and Memory over-commit scenarios.
To look for : I guess there is nothing to look for!! Microsoft needs to improve here.
5) Clustering and Availability
This feature is important to keep your applications up and increase the availability. New windows 2012 offers some great feature like shared-nothing migration that no one offers as of now! apart from there is nothing new. On the other hand VMware offers features like Fault tolerance and Metro Live migration i.e migration across Campuses and long distance with less latency. Share-nothing migration can be achieved , but for this the VM needs to be powered off.
Secondly, the cluster configuration process is simpler for VMware as compared to Hyper-V, where you require various additional steps and validation test to be performed.
To look for : If you arent fascinated by Shared-Nothing Live Migration, vSphere 5.0 is the best choice.
6) Licensing
Licensing cost is what determines your final decision, you need to look at your budget! 
Both licences are offered per processor, though the cost mentioned above may vary from case to case. The cost information have been extracted from the respective vendors licensing guide.
VMware imposes a 96 vRAM entitlement on its Enterprise Plus edition, i.e say you have 2 vSphere Ent. Plus license, then the total memory consumed by your powered on VM in your cluster may not exceed 2×96 = 192 GB. On the other hand Microsoft doesn’t place any such restrictions, just limit virtualization rights i.e Datacenter is the only edition that is allowed to create unlimited VM’s. Standard allows 2 vm’s. The added advantage with Datacenter licence is that, you can run an unlimited number of virtualized instances of Windows Server on processors without purchasing additional licenses. On the other hand, you would require a separate licence for your virtualized instances of Windows Server running on VMware. Though you have some other lower end editions by VMware that might suit you on your budget.
To Look For : If your environment is going to be purely Microsoft based, having windows in your environment would prove beneficial. If you need the best feature along with wide variety of guest O.S support, VMware is the best bet. But wait, take a look at final point before you make the decision!!
7) Miscellaneous
The guest O.S support is and advantage of VMware, VMware supports more than 85 O.S , that hardly any other vendor support, while Microsoft supporting around 25 O.S. Secondly the important aspect from security perspective is the O.S foot print, where VMware cant be beaten. The ESXi 5 only being around 144 mb has a less attack surface area, also its powerfully designed for Virtualization functionality. Microsoft on the other hand being general purpose has a large O.S foot print and attack surface, also the Hyper-V is an added role to the windows 2012 O.S and not specially designed for Virtualization purpose.
Secondly considering the History of organization, VMware has its foot in Server virtualization since 2001 and first virtualization product being designed in 1999. Whilst Microsoft founded in 1975, entered server virtualization in 2008 with first version of Hyper-V. This makes VMware more trusted amongst the end users.
Thirdly. the support for Virtual appliance for VMware seems to be vast as compared to Microsoft Windows Hyper-V.
Lastly the Microsoft history of over-promising and under-delivering, that can be seen from Hyper-V R1 and R2′s actual shipment, where live migration was dropped in R1 and memory overcommit and Hot-add memory/vNic was dropped from R2 release.
The Final Verdict
Though both products offer similar features on paper, what they perfrom in actual decides its success. There have been just assumptions about Windows 2012 Hyper-V 3 and the product is yet to be released. On the other hand VMware’s vSphere 5.0 is already out in the market and used by several customers, tested and trusted!!
You can make the final decision only when the GA version of Windows 2012 is out! But till then I hope this comparison would help you to evaluate both the products and choose the best for your infrastructure, irrespective of the cold war between them