New to the game.
Deadrim
Hey, I just quit WoW (again) and was thinking of picking this game up, but I don't know too much about it. I see Guild Wars and Guild Wars Factions for purchase, which one (or both) do I pick up?
Arya Nibelrund
You can buy both, as they're stand alone products. Factions in chapter 2 of Guild Wars, but you can play it even if you don't own chapter 1. If I was you, I would start with Factions.. then you will get addicted and buy chapter 1 as well 
Canadian Bacon
On the contrary, I would reccomend starting with Chapter 1 (Prophecies). It's alot easier for new players to get into.
Sereng Amaranth
Yes...the original has a slower learning curve than Factions. Be warned, once you begin, you won't stop. Be prepared of at least 2 weeks of all your free time and some of your not-free time being taken by Guild Wars.
felinette
I would recommend Prophecies for the reasons people have already stated. And I agree with Sereng. Kiss your life goodbye for a little while.
ischuros
I am sure he has already kissed it goodbye and sent it off to university, he was, aftrall, playing WoW. Prophecies is the better for the beginer, and it offers a bit more in the way of content. Get Factions for PvP.