Q: What is the best free tool to convert virtual machines (VMs) from VMware to Hyper-V?

A: Numerous tools are available. However, at this point, the Microsoft Virtual Machine Converter Solution Accelerator (MVMC) provides both an interactive and command-line-driven conversion of VMware VMs to Hyper-V, including the conversion of the VMDK to VHD and even remotes the VMware Integration Tools. The MVMC can be downloaded from the Microsoft website.

For a more complete, automated migration experience that scans VMware environments for VMs, prompts you for which ones to migrate, then performs the migration, check out Microsoft's  Migration Automation Toolkit (MAT).