Question in title. This is pretty much what the "PvE vs. PvP" debate boils down to. PvE'ers argue that a world first (We're talking h.Rag/h.DW, not "omg h.Morchok world first!!" is the pinnacle of the WoW-experience while PvP'ers spit in their faces and laugh - trying to explain how Rank 1 is the toughest thing to achieve in World of Warcraft.
So it all boils down to one poll (which is incoming): Which takes more skill: Rank 1 or World First?
I'm putting my money on Rank 1. With the release of the Dungeon Manual (Or whatever the name is), you know exactly what your opponent (The heroic end-boss) will do, when it will happen, and how often said mechanics will occur. From there, it's all a matter of grinding it out, staying awake, and avoiding fatigue.
In contrast, attaining (and maintaining, mind you) Rank 1 is an immensely difficult task. There are hundreds of thousands of PvPers, a wide variety of comps you can potentially face, and no room for error.
Though there is room for debate. If you wipe on a boss, you lose time. If you lose in arena, you lose rating - both of which are pivotal to getting a World First and achieving Rank 1.
So place your bets and show your hands, ladies n' gents. Let's hear some opinions.
-=Edit=-
For those of you who may not have been keeping an eye to the poll....
While I assumed it would be a divisive topic, I don't think any of us were expecting this. A tie with over 600 votes in a poll is a pretty good indicator that there's a bit of a divide in the community..