hello, you won't regret taking an interest in this game. unlike wow, or any other mmo, this game attempts to encourage using skill and tactics in order to get through a mission. primarily focused around teamplay, it is no wonder that the community is at balance between pve and pvp.
all classes are fun, and none are the best - they are all experts in their area. However i do not recommend starting as a mesmer, as they are quite difficult to master for a beginner in comparison to others. Most people will probably tell you that a warrior is a safe bet to start out with, as they can dish out a fair bit of damage and take it as well.
i am not that familiar with WoW, but ill try to explain the classes in relation to it so you get a good understanding
here is a little overview of each class:
Warrior - Melee fighter. This is your typical close combat fighter that goes knee deep in the action. Warriors have a little energy supply so DO NOT use them for spellcasting - but utilise adrenaline to their advantage, which builds up like "rage" in WoW. They have skills in particular weapons - including the sword, hammer and axe
Monk - Usually seen as the almighty healer/protector supporter of the group, if you choose to become one - you will have no trouble finding a group, as you are always wanted. However do not forget that monks can diversify into the smiting damage dealer.
Necromancer - If you like death and decay and lifestealing - this is your profession. this class utilises hexes, life stealing, undead summoning and sacrificing. these classes are quite complex in comparison to more solid professions, but still potent as ever.
Elementalist - what is commonly known as "mage". this class dishes out serious firepower while not really being able to take much of it. elementalists (or ele) utilise fire, water, air and earth to do all sorts of damage to the enemy.
Ranger - I suppose this would be definitely relating to the "hunter" class in WoW. these rangers shoot arrows from their bows, utilising different preparatiions such as poison and laying traps. they also have the ability of a pet, an animal companion which helps them in their travels.
Mesmers - A Class which has the ability of using their foe's spells and abilities against them. in PvP, a mesmer is very deadly and frustrating. however, in pve, they arnt univerally recognised because they are overshadowed by the damage other classes use. Mesmers should be encouraged as they are very capable of saving your life, yet people do not see them at work.
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Assassin - High damage melee character with weak armour. this profession utilises high damaging combo chains in order to completely obliterate his opponent, then when he is done - he retreats to a safe position where he can recharge. DO NOT mistake this class for a warrior - they are incapable of tanking as well as a warrior, and only when you have truly mastered them can you be able to stand your ground in a fight. your objective is to step in (you have the ability of teleportation), do your damage, and step out.
Ritualist - This class makes use of lightning and spirits that he/she controlls to do his bidding. he is very flexible in his ability to deal damage, heal (sometimes better than a monk if experienced D

and protect. This class is quite complex to beginners, as they do not utilise them to their full extent. nevertheless - the ritualist is very very deadly if used right.
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Dervish - Holy warriors. these hooded figures with scythes epitomise the image of cool

. They rely on enchantments to get them through a fight, and deal a LOT of damage as well as take it. they are melee fighters, BUT DO NOT mistake them for warriors. if you rush in - let me tell you, you will get killed. these also have the ability of taking the form of a god, giving them super natural abilities.
Paragon - i suppose they would be related to a "paladin" in wow. these spear wielding angelic like leaders are useful in defense as well as offense. They can dishout a lot of damage while also reducing the overall damage the party receives. these are very useful in a team - and incredible in one with more than one of this class.
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you know what is so great about this game? you are not restricted to one class, gw allows you to picka secondary profession which can be changed constantly. this allows your character to experiment and diversify
for example - a great mix would be a Paragon/Warrior, because both classes make use of adrenaline - the paragon can use the warrior's defense shouts in order to improve his own defense methods