STAY AWAY FROM LINDOWS. If you want me to go into more detail as to why I can, but I'd rather not if I don't have to.
Beyond that, it's all up to what you want to do really.
I prefer Mandrake over Red Hat and it's really good for a beginner. Last time I used SuSE was back around 6.? when it was still free.
If you've got most of the beginner knowledge down, you may want to look into Debian, Slackware, or Gentoo (guess which one I use
)
Frankly, it just depends how much you want to learn about it. I'd say for now, if you're just looking for something other than Red Hat to try out, try Mandrake.
If you want to jump in deeper though and think you can handle it, take a look at Debian or Gentoo.