fear? from your perspective? its hard to say probably every class. from my perspective? no one. Any class can be mastered and embarrass for a living every other class, the person at the keyboard who can push out twice the dmg, clutch with the balance of abilities, and using teammates as damage sponges, keeping them alive long enough to keep you alive with taunts and heals.
long story short? who's to fear? talent that's who you should fear, who should talent fear? no one.
for classes perhaps you want to know what the fotm is so you can roll it and be like yo im good too! but then you still get rolled, (im guessing here btw, and stereotyping to boot). In this case your best best is survivability, and none melee the better.
That leaves you merc and sorc...GL friend. =)