Virtualization for Cloud Computing on OS X

Virtualization of computing resource is one of a key concept for cloud computing.
But what would you select for your "virtualized computing resourse"?

VirtualBox
It is not the best, but is free for virtualization.
"Not the best" in the sense that:
- it doesn't support DirectX-3D acceleration
- frequent updates
- has more issues than the others (VMWare, Parallels)

VMware is known to be better, in the sense that it covers most of the points mentioned above.
And virtualization with VMware can be done free on Linux and Windows.
But not on Mac OS X.

I heard Parallels is even better then VMware on Mac OS X, but I have no experience at all with it.


Ubuntu
Using free-OS as your virtual OS means freedom of its deployment for you.
There are other free-OS options, I've tried several, but found out that Ubuntu is still the best option as:
- It has LTS (Long Term Support) version, which is supported up to about 2 years, compared to other free, open-source Linux distros (Fedora: 6 months, OpenSuse: 1 year, etc.)
- Easy to use (easier than the other free, open-source Linux distros like CentOS)
- Just works (Ubuntu just worked, whereas Kubuntu, OpenSuse with KDE didn't just worked smoothly)
- OpenSolaris will be discontinued by Oracle (ref. here)
- Other BSDs doesn't fully work on VirtualBox.