I think only someone with near-perfect knowledge of both vSphere and Hyper-V could give you valid arguments. Maybe you can find someone here...
Personally, I think vSphere is more "mature" product. I did comparison some time ago, but it was Hyper-V/Win2k8 versus ESXi5.0 so I'm not sure if my findings are still valid. At that time, Hyper-V had no page-sharing, memory compression, and only limited support for memory overcommitment and balooning (only for windows-VM). It was also missing some advanced features of virtual networking (i.e. no distributed switch), some storage-features (i/o control, live migration), and list of supported OS was rather limited (no FreeBSD or Solaris, and only limited Linux support). In addition to that, Hyper-V is not that "light-weight" hypervisor, as it uses Win2k8 partition to manage Hyper-V. Its footprint is much bigger, than that of ESXi. But as I said, I'm not sure if all this is still true.
Concerning price, I think VMware is very competitive with its "Essentials" kits, especially on SMB market. It is pretty much bargain for what it can do, and the price level makes it attractive even for private customers. You could also use arguments as security-record, OS-vendor independency, etc.