To add to what has already been said, iSCSI vs. SMB3 really depends on your particular use case and scale and whether you have an ASA or unified system.
For ASA, you need to use iSCSI. For unified, I like to use SMB3 for very large-scale deployments with many data mobility requirements. Don't forget that you can take advantage of SMB multichannel for improved performance.
For a basic Hyper-V cluster, I would probably just use iSCSI with cluster shared volumes and create your VHDX files on that. Even for larger clusters I would probably still stay with block protocols.
If you plan on using NetApp Shift to flex VMs between VMware vSphere and Microsoft Hyper-V, you will need to use SMB3 for your Hyper-V storage, at least temporarily, as Shift requires NAS storage.
One other point that you must consider is how are you integrating that with other software and services?
For example, Commvault supports NetApp integrated snapshots and snapmirror with Hyper-V, but only with iSCSI and FCP, not with SMB3.
I know this isn't a targeted response, but you get the idea. As with most things in IT, the answer is always, "it depends".
