I use virtual pc (because I still run OS/2 from time to time for nostalgia) and VMware. Overall VMware is the better product, it is much faster than Virtual PC and in my opinion is more stable and requires fewer system resources. ALSO, VMware has clients for both windows and linux, virtual pc is windows only (for intel platforms) since MS bought connectix. I just wish VMware would incorporate OS/2 compatibility. But, I don't see that happening, they dropped it in v3.
I have not tried HyperOS. Does it work similarly in that miltiple OS' are easily switched between? Although it appears to be context switching, not actually running the OS'? Or is rebooting required, making it a very expensive boot manager.