Which VM?

[stan]

I am planing n rebuilding my laptop now that 9.10 is out. I want to be
able to run Ubuntu, FreeBSD, OpenBSD, and perhaps XP as guest OS'es on this
machine. 

I tried this a month or so ago with VirtualBox, and some of these OS'es did
not work under it. I understand that the one Linus is favoring is Xen.

What's the collective wisdom of the list on this? Which VM should I use?

-- 
One of the main causes of the fall of the roman empire was that, lacking
zero, they had no way to indicate successful termination of their C
programs.