I went with VMWare ESXi 4.1 on the advice of a consultant I've been working with. Seemed a bit better for my smaller shop, Boots and works from an internal SD card, freeing up more resources for the actual server operations. HyperV doesn't seem much worse, except for needing the install of Windows necessary to run the VMs, along with MS's arcane licensing and rapidly increasing costs once they've 'locked you in'. You'll find fanboys for both, but they each have their own pros and cons.
