You can basically spot the three different kinds of warriors in this manner ... big 2-hander, arms; two big 2-handers, fury; piddly 1-hander and shield, protection. Arms has always been considered the PvP spec, largely because of Mortal Strike. It was such a compelling ability that Blizzard tossed it into the fury tree, too. These days, arms has a lot more toys to play with and continues to be the most popular spec for PvP. Arms warriors are a healer's nightmare. In addition to Mortal Strike, they have Unrelenting Assault, which combined with Taste for Blood gives them a freakishly boosted Overpower. Typically the bane of high dodge classes like rogues, Overpower practically becomes an on-demand strike ... which makes it extremely dangerous to cast anything for the next nine seconds after they hit you with Rend. Overpower won't interrupt the spell, but it will apply a debuff that reduces spell damage and healing by 50%. Combine that with Mortal Strike cutting healing effectiveness by 50% and ... let's just say that self-healing won't be very effective for a good while after that.
Arms warriors are also more resilient against disarm mechanics because of Weapon Mastery and can mitigate damage taken while stunned through Second Wind. This is why stunning an arms warrior isn't always a great option. Other forms of crowd control are good, but most arms warriors will go all the way down to Bladestorm, which is sort of like the warrior version of a hunter's The Beast Within. They're easy to spot: they're the one spinning around like a red freaking whirlwind! Get out of the way. Seriously, take cover, make as much distance during this period because an arms warrior can deal you world of hurt during Bladestorm. Coupled with a few other talents in the tree, arms warriors can be devastating to a crowd. An arms warrior let loose on enemy front lines and supported by a healer from a distance is crazy fun to see.
It's also good to note that an arms warrior with a lot of rage is simply bad news because of Sudden Death, which allows them to hit Execute even when you're above 20% health, and some even pick up Improved Execute from the fury tree. As previously mentioned, Juggernaut allows them to use Charge during combat and grants an additional 25% chance to crit with their next Slam or Mortal Strike. I think you can figure out just what follows when they Charge you. It'll tickle a little bit.
Despite the balancing act that followed Titan's Grip throughout Wrath, it has become the defining ability of the spec about as much as Mortal Strike stood out for arms. Fury falls curiously behind the other two specs in popularity in PvP owing mostly to very effective protection builds and the obvious advantages that arms offers in PvP. In a way, you can liken fury warriors to fire mages. They're put it all on the line and try to deal as much havoc as they can in a race to the finish. This playstyle is defined by abilities such as Death Wish and Intensify Rage. Specials such as Bloodthirst only encourage the warrior to attack, attack, and attack. Don't be fooled by the healing component of Bloodthirst, nor the regeneration granted by Blood Craze -- they're there mostly to mitigate the penalties incurred by Death Wish and Berserker Stance.
Whirlwind is a fury warrior favorite and is used even against solo targets despite its AoE orientation. Some builds pick up Two-Handed Weapon Specialization from the arms tree and Improved Whirlwind for even more pain. Can you picture yourself getting pummeled by a Death Wishing fury warrior with a pair massive 2-handers? It's not pretty. Fury builds vary greatly in the details, with some builds picking up the AoE snare Piercing Howl. It's not a game breaker, but it's certainly one of the most effective tools in the Battlegrounds, such as inside the Warsong Gulch flag room. Not even all builds will pick up the Mortal Strike-like Furious Attacks -- fury warriors are all about balls out attack and crazy damage, healing be damned.
As tactical as arms plays or as reckless as fury is inclined to be, protection offers a completely different encounter. Protection will mostly be about Revenge, Disarms, and Gag Orders, sort of like a bad B-movie about disgruntled police officers. It's all about control as protection whittles down opponents by locking them down with a bevy of stuns (Concussion Blow, Shockwave, Charge, and even Intercept on occasion), silences and interrupts (Gag Order improved Shield Bash), disarms (with Improved Disarm), and even offensive dispels (Shield Slam). If fury is all about hitting you with a sledgehammer, protection is like killing you with a spoon. Armored to the Teeth ensures they've got some punch to go with their toughness, so they're not entirely without bite, but there's virtually no burst here so it's not something you should worry about. But in a high resilience environment with low burst and where healing is dominant, the playstyle thrives.
Instead of shocking and awing opponents with their damaging abilities, they keep their opponents under control by preventing spells and attacks, stunning and fearing them, and wearing them down eventually. The trick is to manage your own cooldowns to match theirs and unleash burst between lockdowns -- if you're silenced with a Gag Order, be sure to unleash right after. Disarmed? Wait until you get your weapon back and go all out on attacks but don't over commit. If you can heal, get them off between interrupts and stuns. Direct heals work better because HoTs can be dispelled by Shield Slam. The going will be slow, but against a protection warrior, there's really no other way. The good news is that you stand a good chance of whittling them down themselves, mostly because they have no real way to recover lost health.
With warriors, it's mostly about managing your distance and managing their rage. Warriors naturally prefer their combat up close, so ranged classes would simply do well to keep them at a distance. This is why frost mages have tremendous success against warriors. Between their crowd control breaking abilities and a frost mage's ability to root, ensnare, and polymorph, the frost mage can often win out. Even warlocks have a reasonable chance at beating warriors, despite their resilience against fear effects, as long as they manage to pile on DoTs and keep them at bay long enough. The main idea is that warriors have no real means of removing debuffs on themselves. Curses, diseases ... you name it. They'll be a bit hardy against physical attacks, naturally, but they're more vulnerable to magical damage which armor can't mitigate.
They have distance closers, but they're also reasonably kiteable. Ensnare them and go out of range of their Intercepts and Charges and you'll be able to keep them struggling. Smart warriors will whip out a shield and be on the defensive when they're being kited, waiting out the snares until they get within Intercept or Charge range. Don't let them. Bait them into open ground where they can't use objects to block line-of-sight and force you to engage. If you're a melee class, do the reverse and be sure to apply any movement-impairing effects yourself and apply disarms if you can. Warriors are nothing without their weapons, so disarm effects work even better against them than practically any other melee class.
Also remember that rage is reactive as opposed to other classes' resources. It is generated through a warrior's attacks and through the damage they take. The more damage they take or deal, the more rage they generate. This is why some slow burn approaches work well against them, such as DoTs. It will eat away at their health while not generating enough rage. This is why shadow priests have a reasonable shot against warriors if they manage to keep their shields up and prevent the warrior from generating enough rage. Warriors need to use rage because it decays at a constant rate [edit: outside of combat]. Spoil their party by disengaging when their rage is getting filled up, although experienced warriors will keep expending it. A better understanding of their resource should allow you to get a better feel of the tempo of the encounter, and a warrior's rage bar is a good indicator of what they're capable of doing next.
Because World of Warcraft PvP is essentially a complex game of rock-paper-scissors, it should be understood that some classes and specs will have an easier time against warriors than others. Study the way of the warrior and you'll know what they're capable of and even their limitations. And knowing is half the battle.