I highly suggest playing each class until about ~16-20 to see what you like best. There is no hurry to get to 80 in this game. Choose a class based on play-style, not what others say is powerful at the moment. GW2 will go through tons of changes and balancing iterations.
Ranger – Fairly versatile pet class. Pets are nice for leveling in the open world, but die very easily in dungeons. That kind of sucks, as they make up a substantial portion of your damage.
Elementalist – These guys are pretty cool. You can switch elemental attunements ( air, earth, water, fire ) to gain access to different skills and bonuses. Definitely a lot to do here, and they can be fairly complex. They are the normal spell flinging “wizard” type class.
Necromancer – You deal death, plain and simple. They are great at spreading conditions. Their summoned minions seem rather lackluster. Necros can also shift forms into virulent clouds, death shrouds, and liches. Definitely a lot to do.
Engineer – They are pretty fun. They can equip kits that change the skills available to them. You can use a pack of different grenades, throw elixirs that buff/debuff, strap on a flamethrower, etc. They can also set up turrets.
Mesmer – You’re a spellcaster that deals with illusions and confusion. You’re a trickly little kitten.
Warrior – Pretty self-explanatory. You hit things. Hard.
Guardian – They are mostly a melee support class. They give out a lot of buffs and can be fairly tanky. Their range options are limited and somewhat lackluster.
Thief – You hide in the shadows and pop out to do burst damage. They have the best escape mechanisms of any class. Think of them as skirmishers.
