Ok, so from information I gathered in game, I can tell you which class has pros against so and so class, and what cons, but really, this doesn't do it justice, go out in the field and see who you can beat in a friendly PvP match, I'll list them anyway.
Warriors: Pros: Power fighters that can fight really well against range specialists. Ability to learn how to use Guns, Bows and, Thrown. Able to wear up to Mail when starting and up to Plate later on. Against a Hunter, Warriors can normally beat down a Hunter with little resistance. Warriors can beat down a Warlock if he directly focuses on the Warlock himself, even if the minions are weak. A Warrior can beat down a Mage MOST of the time. Cons: Warriors rely on Rage which can only be built up (unless speced otherwise) in battle alone, and it quickly depletes. Warriors can't really beat down a Shaman, since, even though Shamans only wear up to Leather, can range, close combat and, heal themselves, and put out Totem buffs, which at higher levels, provide a challenge to Warriors. Against Priests, Warriors have the time that cannot be so easy, Priests have mild DOT spells (damage over time) can protect themselves and heal themselves, even if they wear cloth only. Paladins are mixtures of Warrriors and Priests, and can wear up to Mail like Warriors when they start off, so Warriors can rarely, if ever, defeat a Paladin. Warrior versus Warrior is a long and hard battle, one person will normally be better then the other, since Warriors have the same moves as they level up. Warrior can defeat Rogues, but when they get to high levels, Rogues can turn the tables in the middle of the match, or just give the Warrior a hard time. Even the impossible can happen when a Hunter's pet comes in and finishes the Warrior before they notice the lackage of health, even if the Hunter sucks at close combat, they can, sometimes, strive against Warriors. Hunters: Pros: Hunters start off with the ability to use Range weapons, and have 200 ammo. Hunters have stings and shots that can be very helpful before the enemy gets in close and personal. Hunters, at level ten can tame pets and use them in battle, like the Hunter, pets level up. At first, Hunters can only wear Leather, which is a downfall at first, but as they get more and more experianced, they fit into Mail and get used to the ichyness. Little joke, but still good, right? Against a Warlock, the Hunter doesn't suffer much if he/she stays his/her distance. Pet Pros: Whatever stats the Hunter has, the pet has for a boost, but early con, it's fractioned into their first off stats. Whatever resistances the Hunter has is fractioned into the pet. Each pet is unique, and can us abilities that a Hunter can train them for (i.e. A wolf has an ability, most of the time, bite rank one or higher). Cons: Since Hunters have to rely on Magic power to use all of their skills (besides auto shot and attack) they have to have high Magic power to survive. Most classes have little difficulty with Hunters, since they have close combat cons too. Even though, when a Hunter gets the Flare ability to show cloaked in a 30 yard radius at level 20, Rogues can still use sap and then ambush the Hunter before they know what happens. Hunter versus Hunter, like Warriors, the battle is long, but since just about everyone is unique and Hunters normally have different Cons and Pros according to their playing style, one Hunter has an advantage over the other, pet wise is also the same, since they pick up their masters power and stuff. Pet Cons: Since pets use a thing known as Focus to use their abilities, they have only 100 focus, no matter what level they are, and sometimes waste it carelessly. You are the pets master, and they expect to be fed, if you don't feed your pet, then your pet runs away, that is something a Hunter doesn't want, and normally spend a great ammount of money for (food wise). No pet is perfect, and they might have more health then you, but have less defence, so you sometimes need to increase your stuff in one catagory when you don't need to, for your pet.
Those are the only two classes I'll list for now, but stay with me, and check often to see the rest of this guide (not a real guide)in the fractions it is in.
Druid: versital hybrid, unique in the fact that it can fill many roles more successfuly than other hybrids. Has the ability to shape shift into many different forms including cat(dps mode), bear(tank mode), normal form(Dps magic and healing magic), and water and land travel modes (cheeta and walrus). Best primary professions professions: leatherworking and skinning, alchemy and herbalism.
Hunter: excelent solo class, unique in that he/she can train almost any animal in the game to be it's pet, also only class with a an auto-shoot for guns and bows. Best primary professions: skinnning and leatherworking, alchemy and herbalism
Mages: range dps and Aoe class. Fights best with his/her enemies far away. Limited by only being able to wear cloth armor, but one of the only classes that can use wands. Best primary professions, Alchemy and herbalism (for survivability), Tailoring and enchanting ( making your own armor and making money selling enchants).