I'm using Debian.
At first I just want to say, that Windows is still the best operating system for newbies and it has the best, most confortable desktop of all os I ever tried, nothing beat it
But if you want to try something new, I would recommend Arch as Xijesu said or Debian (my fave distri.) which has all what a linuxsystem needs. But on the other hand it could be really hard for newbies to use the terminal, because it's very powerful tool and needs a little bit of volition to learn those things, ofc the basics as apt.^^
If you don't want to install it as your main OS or you're using already four primary partitions you can boot from a livedisk and test it some hours. Or you buy a RaspberryPi, which is a very nice thing for newbies@linux^^
