I feel you should stick to a more damage dealing class, rather than a Mesmer, Necro, Monk or Ritualist.
Assassins are usually considered weak and are rumored to die in a matter of seconds. This is not true. I clever player can teleport in, do a bit of spike damage, and teleport back without taking a hit. During PvE, finding a group for missions is a hard life as an Assassin, generally due to this stereotyping that goes on amongst other classes. The way they're considered weak is ridiculous. A Ranger being hammer spiked will die just as fast as an Assassin being hammer spiked. Do Rangers get kicked out of mission groups to make room for a Mending Warrior? Nope.
In PvP however, the Assassin is treated completely different, atleast for GvG that is. In a single GvG, a single undisturbed Assassin can wipe out an entire base of NPCs without even blinking an eyelid. GvG is the main use for Assassins, and for single target spiking. However, popular skills and attack chains that deal vast amounts of damage with little thought, will often be nerfed.
To sum up, being an Assassin in PvE is tough, but if your willing to Henchway to level 20 and then be ran to the popular spots, and are willing to pay for the skills, then go for it. Being an Assassin in general PvP is okay, however for the true Assassin feel, go for GvG and gain the experiance of pooning a base of NPCs or pooning an unprotected flag runner.
Elementalists are extremely popular. They get accepted into groups without being asked their build, and will never go out of style. As a PvE Elementalist, you can fight your way to the end of the game without the chance of not finding a group. Lots of spike damage, lots of AoE damage, and lots of spike damage. I know, I've mentioned spike damage twice, but there is so much damage! You can set groups of enemies on fire, freeze them inplace and then send in a shower of meteors to finish them off.
For PvP, there are many Elementalist builds out there, and I don't know too much about them all, but Elementalist is definately a contender for the top class.
Ranger

. My favourite. You can do just about anything with a Ranger. For PvE, you can make money running people places, or you could do it for free just to be nice. There are many PvE builds that are effective, but the most popular in most in-demand is the Barrage Bot. As a Barrage Bot you will almost never get turned down for a group. If you do get turned down as a BB, then switch to Interrupt! Rangers are here and here to stay, play a Ranger today!
PvP wise, Rangers are worth while all over. In Random Arenas, you can play Interrupt to annoy that Healer Monk, you can play as a Trapper, to annoy that group of melee fighters over there. The possibilities are endless... The most known PvP build would have Cripshot. A Cripshot can solo a base of NPCs not quite as fast as the Assassin, but just as effectively. When teamed up with a Melandrus Arrows Ranger, you will be causing -7 Health Degen to almost every foe in the area. Play a Ranger today. I almost forgot, Ranger Fow armor is the bee's knees.
Warrior. I can't be bothered to explain the different ways to slay those lone casters sent off the bring the flag, but Warriors are good. Maybe theyre basic? I don't really know. From what I've been told, playing as a Warrior and being effective in a GvG takes co-ordination, speed and lots of DPS! I don't want to recomend playing a Warrior, because there are many out there.
I'm going to bed
