Clean installs directly from the repos...
Using libvirt (virsh/virt-install/virt-manager) you can install from the HTTP repo of a Linux distribution to be super lazy. During installation you simply provide the URI in the location field or tools like virt-manager will have an option in the wizard.
For Debian you would use:
For CentOS which lacks a CDN mirror or I could not find it quickly, you can try: