macOS as a guest and in the host I want to install macOS High Sierra as a guest having macOS in the host but want to know what virtualization software either VirtualBox of VMware provides the best security options between Guest and Host.

For example, I would like to create multiple VM's with their own disk encrypted (filevault) boot/firmware password or any other Guest mechanism in place in a way that when the VM is down, the host could only delete the VM but in no other way could see contents of the disk besides probably brute forcing it from the host console.

The access to the guest VM may be via VNC/remote desktop/ssh but they are on a shared environment (rack with multiple mac minis) in where some extra security is required at least when VM's are down since once UP could be very easy from the HOST attach to the console.
This would be trivial with either suggested VM software. 

Make an encrypted sparse disk image large enough to hold the guest storage and then build your VM once you’ve mounted the secure disk image. 

By controlling the encryption passphrase of that store, other admins can only delete the container, not mount and read it.