My nominees would be;
Elementalist
Air Magic: Lightning Surge {E}
* The monsters are either too stupid to care about damage spikes, or it's not likely to matter. This spell has absolutely no effect on bosses- The half hex time causes it to run out in 1.5 seconds, short of the required 3.
Earth Magic: Iron Mist
* Snares tend to be some of the least useful skills in PvE. Just aggo them to the tank, it's fairly simple. If you're running as a Geomancer, snares actually serve a purposel They make you faster than the enemy, which causes them to ignore you when you run away, as they can't keep up.
Iron Mist got the slot because unlike other snares, it's not AoE, and it can be problematic while grouping (OMG! HAXX! Invincible monster cheat!).
Energy Storage: Ether Prodigy {E}
*It just pales in comparison to Ether Renewal. I suppose I could say Aura of Restoration instead, as the healing is not enough when you're being pounded on to matter, and is otherwise wasted when you're not. Aura of Restoration, however, is compatible in Ether Renewal builds, and Ether Renewal is actually very good.
Fire Magic: Searing Heat
*5 seconds duration, 25 cost, exhaustion, and the same damage as all of the other DoT fire spells? What in the world were they thinking when they made this spell?
Unlinked: Glyph of Renewal {E}
* Even not in PvE, I don't like this one. Spells tend to either have too long a recharge time for the halved duration to matter (the battle will probably be over), or they recharge too quickly and it's not needed. Arcane Echo and Echo tend to dominate in the multi-casting department, though they're not elementalist skills.
Water Magic: Mind Freeze {E}
*This one wins for the same reason as Iron Mist did. Although there are other single snares, this one has elite status for some odd reason. A good chunk of the water line is fairly pointless, in reality though. Monsters will try and stick to you like glue already, and if you don't want them to, moving around your tank properly will place the aggro on him instead.
Mesmer
Domination: Mind Wrack
*Should be fairly self-explanatory.
Fast Casting: Mantra of Recovery {E}
*To be fair, it's also the best Fast Casting skill.

Illusion: Ethereal Burden
*Same reasoning as the other snare choices. It beat out Crippling Anguish and Imagined Burden because those actually can be used to kite enemies in soloing. If you choose a type of enemy that travels in groups of 3 or less, you can degenerate them to death like this. However, Ethereal Burden is too slow to cast, and takes too long to recharge to really help.
Inspiration: Ether Lord
*Hands down, it wins. The energy stolen isn't great, it has half duration on bosses, and it causes you to lose all of your energy.
Unlinked: Epidemic
*Adjacent range, and the original enemy loses their condition to boot. You need at least 2 monsters in range to make it do anything more than merely swapping the conditions, and it costs 15 to boot.
Monk
Divine Favour: Divine Healing
*Was a hard choice, but in the end, I went with this. That 60 second recharge is killer, and you have to be nearby, which could potentially lead to aggroing monsters to you. The 2 seconds casting time means it had better not be an emergency heal.
Healing Prayers: Live Vicariously
*If it's yourself you're putting this on, why not Vigorous Spirit instead? If it's your allies, and they're hitting the monsters, aren't they the ones most likely getting hit? And if so, I don't think it's you that needs the healing. I was considering Heal Area, but monster AI is fairly predictable, and positioned properly, there're few to no drawbacks to it.
Protection Prayers: Vital Blessing
*Set health bonus. Whoopee. It's not going to make healing any more effective.
Smiting Prayers: Holy Wrath
I'm not sure how some monsters manage to continue healing while maintaining Holy Wrath, but the only thing you'll be able to do is maintain another 3 *enchantments and use signets. Holy Wrath can sap an elementalist dry in no time flat. Assuming you use Watchful Spirit, Signet of Devotion, Mending, and Retribution with this, you'll still have trouble taking out small groups of monsters; They have to damage you a little over their health to get killed, and their combined health totals way more than yours.
Unlinked: Holy Veil
*Doubles hexxing time. Doesn't stop any, just doubles the casting time.
I'm done for the night, too tired to really think well anymore. I'll edit this if I remember. [Was relaxing though. o.o]