It really depends what gamemode you want to play the most, but since I am a PvE player so that's what aspect of the game I will mainly cover.

Necromancer

Necromancer is a class focused around dark magic, and conditions, though power builds on necro are totally viable and also just as fun to play. It is a high vitality class with a professionskill called shroud. The shroud replaces your health bar and provides you with 5 new skills. Cons with necromancers is that they are fairly immobile, tough they have the possibility of perma swiftness necros can feel somewhat slow.

Elementalist

Elementalist is a class focused around controlling the elements. An elementalist can literally do everything in my opinion. They have extremely strong condi and power builds, a lot of mobility and huge aoe abilities. Cons with elementalist is that you are really squishy, so if you don't build for survivability you will find yourself dead on the ground fast until you learn the class properly.

Mesmer

Ah, mesmer is the illutionist of the game with a great amount of their game play focused around illusions and controlling your opponent. With a mesmer you will get a great ammount of mobility and high damage with shattering illusions and bursty abilities. The mesmer mostly shine in PvP but I have found a ton of fun with it in PvE Cons for the mesmers are lack of damage over time. And same as for the elementalist, if you screw up you are not the most tanky guy in Tyria and you therefore have to play with caution a lot of the time.

Thief

If running stealthy around in the world and surprise attacking your opponent sound fun, then thief is something for you. The thief have extremely high burst and the highest mobility in the game. Especially in dungeons thief's are highly appreciated of their ability to stealth an entire group and then pass the enemy in no time. The cons of thiefs are that they lack a good ranged weapon atm (we'll see what they get with HoT) and they are not the tankiest in the world, eventough they have fairly good survivability.

Ranger

If you enjoy running around the world with a companion by your side then ranger is something for you. The ranger has the ability to control a pet which can be really great once you learn how to get the aggro from the npc over to the pet. My first lvl 80 was a ranger because you can pretty much solo everything once you learn the class. The cons of ranger is that they don't have a great function in bigger groups with such as aoe might or stability.

Guardian

If you enjoy healing and providing support for your group while you deal tons of damage yourself then guardian is something for you, with extremly high base healing and damage the guardian is something that suits everyone, though its a pretty locked class in my opinion in which you can't push the limits of the class too far. And guardians also have a small health pool to compensate their great healing.

Warrior

Most people new to the game enjoy warrior the most as it is an easy class, with great damage, high health pool and a LOT of weapons to choose the warrior can't go wrong. You also have the ability to spam out might and other empowers to your allies.

Something you may have noticed is that I didn't write anything about the engineer, that is simply because I haven't gotten anyone to level 80 and it would therefore be foolish to act like and expert on the class, regardless I hope you enjoy my post and hope you stick around in the game for a long time. If you have any questions feel free to ask me, Rockefaar.9281