Agree with Alan, I see little value in recording this if you have even more than 1 hypervisor host because VMs generally are going to move around.
The individual host a VM is on usually doesn't matter from an operational point of view. I think vCenter, SCVMM and Proxmox all support showing VMs across a cluster in one place. You can record the Cluster info in the make / model fields of the VM asset and it shows up fairly decently.
Services isn't a bad choice either if you really do want to record this. It's a bit more flexible in allowing you to just link a load of stuff together to show different relationships.
