Best VM to use on opensuse 11.2?

I need to install Ubuntu but I would prefer to use a Virtual Machine to do it so I can run it inside OpenSUSE. I have virtual box installed but have heard about Xen and others. What’s the best VM to use? Which works the best with openSUSE and runs the most efficiently?

Virtual Box - No hesitation

Virtual Box (Sun Version) Install HowTo - openSUSE Forums

Using Virtual Box - Some Quick Tips - openSUSE Forums

Virtual Box. idem

Thanks! Will do.