At the moment, until next major content patch,
shamans have the
least survivability of any healer. They also have the
worst mana efficiency and the
least burst-healing power. However, elemental at the moment is a powerhouse in 5v5.
Elemental Shamans are basically the equivalent of Destruction warlocks
(Warlock trees : Affliction, Demonology, Destruction).
While
Destruction Warlocks have greater offensive potential than elemental shamans, elemental shamans are generally placed on teams for
bloodlust (which grants 30% haste for 40 seconds every 10 minutes, or once during a standard arena game, or multiple times during long games.)
Mages have never been
fotm (flavor/feature of the month) for extended periods of time. Although arcane had been overpowered during the beginning of Season 5, mages have never been
the overpowered class. However, mages have a lot of potential, and in the hands of a skilled player can be
the biggest asset to a team. Mages, although not having the on-demand burst of a warlock or elemental shaman, have
amazing cc (crowd control) capabilities. A single mage can keep multiple people locked down by means of
Deep Freeze (ranged stun),
Frost Nova (root),
Polymorph (Very good crowd control that turns target into a harmless animal), and
counterspell (Silences for a few seconds, and interrupts that type of magic spell for 8 seconds).
Priests and Paladins are generally used to dispel magic effects such as polymorph and other magic effects, but if you are cc'ing the only dispeller of a team, or are locking down the dispeller while you cc the rest of the team, you can control the game as a mage. Mages at the moment, are most popular in rmp (Rogue, Mage, Priest) because of its crowd control and survival capabilities.
A good mage can stay alive very well. A mage can keep melee enemies away by use of frost nova, and their water elemental's frost nova, and also can
blink, which is basically a short-range teleport. Not only this, mages can stop all types of damage by deepfreezing, and counterspelling dps (damage dealers) and healers. Also, all mages have
Ice Block (which makes the mage immune to all damage, but the mage cannot move or cast inside the block), and a frost mage has
cold snap which refreshes all cooldowns, so that they could
ice block twice. Not only this,
mirror images (basically clones yourself making 3 allies that do not hit as hard) drops the enemy's target, like feign death for hunters. So basically, if people go on you, you can deep freeze a damage dealer, counterspell their healer, use mirror images to make everyone untarget you for a second, then shatter the person in deep freeze for an enormous amount of damage.
http://www.wowhead.com/ is a good database for information if you want to look up spells.
You will want to go to http://www.wowhead.com/?talent to see all the different talents/specs for different classes if you don't understand what different specs such as frost or destruction mean.
Destruction Warlocks right now are
not very popular in smaller brackets (2v2,3v3) mostly because they are locked down fairly easily. However, in 5v5, where they have a greater chance to damage targets, they can shine. One of their greatest tools is
Shadowfury which is an aoe (area of effect spell) that stuns everyone inside for 3 seconds. This is a huge advantage in every bracket that a destruction warlock plays in. The other main spells are
Immolate, Conflagrate, and Chaos Bolt. Warlocks generally burst using these three spells. Conflagrate does more damage with immolate on the target, and chaos bolt is the basic burst spell. So basically what you will do as destruction is try and fear people around.( Fear is a crowd control that makes people run around with no control over their character until the fear effect time runs out, or it is dispelled by a priest/paladin/tremor totem by shaman.), then Immolate to put up the damage over time effect, conflagrate to eat the bonus off the immolate spell, then chaos bolt for a huge amount of damage. This can also be followed by a death coil (which is basically a fear that does not share diminishing returns with other fears), or can be started or ended with a shadowfury, to stun the target or targets in place.
However, next major content patch you will probably see more warlocks playing as affliction. (You probably won't be geared at level 80 until next major content patch anyway, which is season 7). Affliction relies more on damage over time spells. Often, you can put dot effects on multiple people, putting up a lot of pressure. Because this would be gimped against priest/paladin teams that can dispel magic effects, affliction warlocks have a spell called Unstable Affliction that damages and silences anyone that dispels it. Because of the random mechanic of dispel, this is very powerful, and dispellers generally do not cleanse people that are afflicted by Unstable Affliction. Generally Affliction warlocks will dot up multiple people, generally utilize fear to a greater extent than destruction warlocks, then get someone low (around 50%), then death coil (short horror effect that is similar to fear), haunt (affliction burst, and increases damage of all dots on target), then soul drain (ticks for 4k-7k every dot tick when target is under 25%).
However,
warlocks are very reliant on their pet. Generally, warlocks will use a felhunter (affliction or destruction) or a succubus (destruction). Seeing a succubus is somewhat rare in pvp as they are easily killed. However, healers can heal a felhunter through moderate damage, unless a team tunnels it (damages it for a long period of time). However, next major content patch, felhunters will have a greater amount of health (25,000-30,000), and be affected by resilience, which is the major pvp stat of WoW.
I would not recommend moonkin, or caster druid for serious pvp.
A skilled hunter is basically as valuable as a mage. All three specs for hunters (survival, beast mastery, and marksman) are viable for pvp. Survival is based around Explosive shot (fire damage) and wyvern sting (poison that sleeps one target for a period of time). Marksman is based on chimera shot (damage based on poisons) and silencing shot. Beast Mastery is heavy burst damage based around pet and "big red" or The Beast Within.
This season, season 6, Warlocks and Hunters are very weak. Mages are somewhat alright.
Right now, classes such as arms warriors, restoration druids, discipline priests, protection healing paladins, unholy death knights, frost death knights, and rogues are powerful.
However, next season, with the next major content patch, classes such as warlocks, shamans and hunters will probably be more powerful.
Additonal Information
MS = mortal strike = effect that lowers healing by 50%
Warriors = Mortal Strike = Physical
Hunter = Aimed Shot = Physical
Rogue = Wound Poison = Poison
Curse = Purple Icon = Used by Warlocks
Dispellable by Mages, Druids, Restoration Shamans
Poison = Green Icon = Used by Hunters, Rogues
Dispellable by Shamans, Druids, Paladins
Magic = Blue Icon = Used by all casters
Dispellable by Paladins, Priests, Felhunters (warlock pet)
Disease = Brown Icon = Used by Death Knights, Priests
Dispellable by Shamans, Paladins, Priests
If you're looking for serious pvp, watch some good pvp videos. I would not look things up on youtube, but research who are the most famous WoW players and see their playstyle.
Popular Warlocks = Brayzee, Azael, Glick
Popular Mages = Pookz, Orangemarmalade
Popular Hunters = Megatf, Twixz
When looking up famous players, look at top arena teams that have competed in recent tournaments (A good one to look at is MLG), and look at teams such as:
Pandemic
eMazing Gaming
Fnatic
Complexity
Evil Geniuses
Ensidia
Gravitas Gaming
SK US
Celex Mage Video
http://warcraftmovies.com/movieview.php?id=106145
I would not follow every video on warcraftmovies because most of them are not always the best. However, if you find a really good one, you should download it instead of just watching the stream, because streams are generally low quality and it's hard to see what's going on.