This is the topic of nearly half the threads on the WoW forums. And everyone's response to this question is in response to their gear. This is only half of the answer.
When leveling your Warrior, there is only one answer:
Arms. Your gear choices are limited when your leveling up, and Fury is too stat dependent to be effective at any level other than 80. Even after hitting 80, Fury will be sub-par compared to arms for quite some time.
But with Conquest and Triumph badges, the jump into fury level gear isn't that hard to accomplish.
The numbers you want to shoot for to make fury worthwhile are:
164 hit (minimum)
any expertise is helpful
4000+ AP unbuffed
213+ dps weapon for your main-hand.
If you don't have these numbers, Arms will probably give you more personal DPS. But both specs with
max gear are evenly matched.
And now for the readers who are well beyond those limits.
This blog is directed to the raiding DPS warrior. What spec will be most effective in the raid environment? Lets break it down.
The first question you need to ask your self is what buffs are already covered by other raid members, and what does the group composition look like? Chances are you will be the only DPS warrior in the raid. So you have a choice between 2 DPS specs.
Blood Frenzy (Arms)
vs. Savage CombatBoth these talents do the same thing, and do not stack. If you're raid already has a combat specced rogue, then your Blood Frenzy Talent will only provide you the 10% attack speed buff. So check with your rogues and see what specs they are.
Trauma (Arms)
vs. MangleThese do the same thing and do not stack. If your raid has a feral druid tank he will be doing mangle for threat anyway. However, if your raid has a dps kitty druid, let him know that he doesn't have to use mangle anymore since your arms talent already provides that buff. He will be very happy.
Rampage (Fury)
vs. Leader of the PackYour Rampage talent is overwritten by the feral druid's talent. 5% crit is a lot, and the raid needs this. If your raid does not have a feral druid, it falls upon you to provide this buff. It trumps both Blood Frenzy and Trauma in terms of need-a-bility. (Yes that's a word =D)
In conclusion...If your raid group does not have a feral druid, you should be fury.
If your raid group has a feral druid, you should be arms.
If your raid group has another dps warrior, then choose the opposite of him.