vm hypervisors, my conclusions at the moment

Best for Windows host OS is Hyper-V. Best for Linux host OS is KVM.

VMWare Server 2.0.2 was the last I worked with, quite already long ago. More recently some trial of VMWare Workstation, but only very superficially. It seems that all that it is currently good, is probably their baremetal hypervisor, which I didn't try, but both their OS-based hypervisors for Windows and Linux are inferior to Hyper-V and KVM respectively.

VirtualBox is best as just a toy, for entry-level virtualisation if you currently know nothing about this topic, or if your goal is just a very temporary sandbox where you want to quickly mess up with something relatively small. Also on the bright side is that you can passthru an arbitrary USB device from the host to a VM and treat it as if it is physically plugged there, very handy if you develop/test a device driver for such hardware.

YMMV of course, depending on what you expect, but my personal conclusion is this.