Best on 1vs1?

[TWolfeIA]

Death Knight would be the best, IMO. Too much you can do to lock down any given class. Warriors and Rogues sometimes have a chance if they play VERY well with equal gear. I spend a lot of time dueling in order to feel out the classes I don't know, and It has gotten to the point where I spam trade offering 500g to anyone able to beat me in order to get people to try.

Pros
Lichborne fear immune/DC Heals
AMS vs Casters/Fear/Misc CC Also gibbs Paladins and fuels DC spam.
IBF Stun immune Ghoul stun a rogue on their open, pop IBF before Kidney Shot.
Strangulate to zone in on casters in order to save DG, also good to gibb paladins and other DKs before they get momentum.
Ghoul Sac
Ghoul Stun
Gargoyle's passive pressure
AOE Slows
Chain CC with no DR
Much more..

Cons
Cannot fly while in combat.

P.S. Loldeathstrikespam

[Haibara]

Block capped prot warrior... Just no fucking way to get a cast of

[Sølidus]

DESU

[K4ge]

Hmm lets see rogue:

Fails against Paladins (all specs)
Fails against Feral Druids
Fails against Arms warriors (assuming they're decent)
No chance at killing Disc Priest or Resto druid (probably die from thorns)

Fair against Mages
Against another Rogue if you dont sap first, you lose (luck dependant)
Hunters will mess you up if they get the jump on you

Beat DKs (mainly because none use the disarm runeforge)
Beat Locks
Beat Shamans

Rogue is great at killing/ganking undergeared players in BGs, yeah they are. But assuming its an equally geared, equally skilled 1v1 I'd say its hardly reliable. And if you are one of those guys who trinkets out of cheapshot then you deserve to get killed.

Wroing. Fails against locks, and mages, can however kill arms easily.