Now that both Microsoft and VMware have officially announced the new released of their virtualization products it’s possible make an homogenous comparison between Hyper-V 2012 R2 (the fourth generation of Hyper-V) and vSphere 5.5.
VMware vSphere 5.5 introduces several news and scalability improvements, on the other side Microsoft Hyper-V 2012 R2 consolidate its features and improve what was already existing in the 2012 version, with a limited (but significant) new features. For example now, finally, some VMware old date features are mainstream also in Hyper-V, like VM hot cloning, hot disk resize (in this case also with the possibility to reduce the size).