Assassins are the easiest class to get killed by playing wrong. If you've just started playing GW, then yes: they are the worst thing you could start with because they have the steepest learning curve. They don't forgive mistakes.
Paragons are the most nerfed in recent memory (that doesn't make them a bad class at all; it just shows how unbelievably powerful they used to be). I'm including the necro energy management nerfs in that statement; Paras got slaughter-poomped by comparison. And yet, HA still sees balanced builds with paragons holding halls. Paragons second warriors in terms of armor. Its a no brainer to see the appeal of the class. At least it should be. i blame whining and bad farm capability on the classes loss of appeal.
Mesmers are the most misunderstood and underrated by people who don't know better (PvP: mesmers dominate; PvE: try Duncan with and without one then talk). People ignore the power interrupts give to the game because direct damage and direct healing is easier to understand. A mesmer interrupting an SF cast in either PvP or PvE is a powerful action. Not only does it have the capability of damaging your opponent (armor ignoring damage that can range over 100) it reduces the damage that backline characters need to heal. That same mesmer shutting down a monks Aegis (AI monks use Aegis now


)? its should be pretty obvious to even the most ardent detractors that interrupting skills and spells have a place in the game.
In either playstyle, good disruptive capability is a double threat. Fools don't see that (meaning no disrespect...well, maybe a little disrespect

). Most of the better players I know that are using Gwen aren't just using her because she looks nice.
While I said sins are the easiest class to get killed by playing wrong, they are not the hardest class to play. Human mesmers do not have the server ping and reflexes of AI. They are largly disrespected because they can't powerblock a reversal of fortunewill. But where they excel beyond AI is threat analysis. The truly good ones know what they should shut down to help the team the best. It may be the monk. It may not.
But a bad mesmer probably won't die missing interrupts and shutting down the wrong target. She'll just get other players killed doing it.
Ritualists are the most misunderstood and underrated by players who should know better. Lots of whining in game about rits being too easy to play=rits are a far more powerful class than people give them credit.
Necromancers? Comeon; half the hero builds I see people run require an SS or MM in PvE. Their hex spam has nearly broken GvG meta and they've always had a place in HA PvP.
Dervishes...have broken the meta twice now. Grenth's dervs destroyed heavy enchant builds. Melandru dervs are still kicking. If you like to PvE tank, run an Ebon Dust Aura derv. The damage they prevent is often more than anything a warrior's armor can boast. While they can't extend into a backline the way wars can, the damage output makes them fearful in pvp even after the avatar nerf (and nerf and nerf...and nerf).
and Rangers? Ask a monk or a runner if rangers suck in PvP. Run a R/Rt in PvE (splinter and barrage can outpace many AoE caster builds). I think the disruptive aspects...I think I covered that with mesmers.
The rest is whats called the "holy trinity" Warriors, Monks and Elemenalists. Easy to see what they can do, and they do it quite well. They wax and wane in popularity, but there is almost always a place in a balanced build for these three characters.
Are any classes "the worst"? In the end, I say no. They are all good at doing what they do. The real question should be: "what do you want to do?" Most class bias is based on the other players expierience with the class. if they sucked at it, you must also...or else they might not be as good as they thought they were
So do what you want to do and play the class you like to play. Some players will scorn your choices, but you know their dirty little secret (most of they suck; if they won't invite you its a good thing for you...because when the team wipes after they did invite you--and messed up--its you they'll blame). Some will see your skill and want you in groups--playing what you play. those people make friends, make guilds, win tournies and farm phat lewts
GGs