Hate to be so narrow.. but anyone who didn't say Linux Mint as the best New User OS is wrong
Seriously it's very close to the windows design, many PAIN in the necks like Flash / office / Java / ect.. are already installed (albeit may be out of date, but the updater does the work for you...)
The reason LM is the best is because it comes with these preinstalled... the most difficult thing for a new user to do is install a OS and the first thing you have to do is Jump into a Terminal to type out Code to get things working. With Linux Mint you install and then go watch your favorite youtube video or whatever you crazy kids do now adays...
Keep in Mind with Linux Mint many Ubuntu Articles for Fixes or troubleshooting will work just the same on Linux Mint. (LM is based on UBUNTU, although they are making their own way in the world as well).
Once you got 3 months under your belt and feel comfortable install Virtualbox and use it to try out other Distro's of Linux through this Virtual Machine..
VM"s run faster & smoother then USB Bootup's and gives you a better feel for it.. Also you can run it INSIDE of your OS so no rebooting junk just to try out a OS.. you can have multipel OS"s running at once with Virtual Machines..
I suggest once you get your feet wet with Linux Mint then try out Other Smashing Distros like:
Fedora (Based off Red Hat Unix server) this is the cutting edge Distro lots of eye candy and supports latest & greatest
Ubuntu - Linux Mint's based on Ubuntu you should feel at home and try out their Unity bar for faster access to Apps
OpenSuse - another great Distroy that is similar to Linux Mint
Some Terms
KDE - means it has a windows "Style" Start menu at the bottom left Hand corner
Gnome - Means it uses the Traditional Top left Corner Menu you find in Classic Linux OS"s
LXDE - Version of a OS means it's men't to run on slower/older machines for better performance you miss some of the fancy of the normal versions.
When you install Linux Mint, Once you log in you will shortly after get a notification that you have updates (like ANY OS lol) please install these first to get started updates are ALWAYS important
Enjoy!