QEMU is fantastic. I think for spinning up a VM just to try out something, virtualbox is still a good option because of its gui and its simplicity. QEMU is extremely powerful however, and I'm glad it exists.
It's a bit of an apples vs. oranges comparison though. AFAIK Virtualbox is a hypervisor for x86-64 only. Qemu, otoh, can emulate a number of different hw platforms.