(for the record I've done some Linux KVM/Libvirt management of VMs on servers so I'm not entirely without a clue, but VBox runs everywhere I am and is my go-to for low value messing about, especially now that all that stuff has long ago fallen out of my head. If I had to do anything serious or non-interactive I'd not be looking at VirtualBox for it.)
VirtualBox, VMware and Parallels all offer much better shared folder options that are built in.
Virtualbox is one product, one package. That’s easy to sell, install, understand and google when you need help.
Virt-manager, libvirt, QEMU and kvm... Takes more time to understand, and googling it when you need help requires you to partially understand it. Kinda chicken and the egg.
Also with Vbox I get the VMs desktop scaling to my Vbox-window, as opposed to the other way around, which I get with QEMU. That still annoys me slightly.
Other than these somewhat small things qemu is the fantastic, much appreciation for your work!