Linux!
My prefrence is either Knoppix 3.4, or Slackware 10. Both are highly portable, but not all that user friendly.
And as for the differences between the two:
The main reason why people use Linux is because of the completely open source software. Linux and all its programs are 'free' as in freedom, meaning that you can go in and change anything you want to about it, as the source code is included. There are many different versions of Linux, called 'distros' (as in Knoppix and Slackware) Linux can play 'nice' with Windows, meaning you can have both on the same system, if that's your thing. It was made by Linus Torvalds in 1991, and is based on the old UNIX systems (
LINus
UNI
X)
Windows however, is more focused on being user-friendly, and sort of locks down on its programs so that users don't get too confused. Which can be a good or a bad thing.
Linux is usually run as a CLI (command line interface) where you use a text based interface to get what you want done. There are, however, two popular GUI (graphical user interface) that some Linux users prefer to use.
KDE Screenshot:
http://www.kde.org/screenshots/images/3.2/snapshot02.png
GNOME Screenshot:
http://www.gnome.org/start/2.0/screenshots/csm-desktop.png
There also is a desktop made only for Redhat Linux and the Fedora Project, but since it seems to be a minority in the GUI's as of now, HBB won't bother to include it.
Thank you, and Goodnight