The differences all depend on spec, of course. Two classes with different specs will seem like quasi-identicals most likely. A protection warrior and a dps shadow priest doesn't exactly have good synergy (their spec is much more friendly with other casters), so they'd turn out to be Conflictors, but a protection tanking warrior and a healing holy priest would naturally be duals.

Warriors: ESTps & ESTjs
Rogues: ISTps & ISTjs
Priests: INFps & INFjs
Mages: INTps & INTjs
Hunters: ISFjs
Warlocks: ENTjs
Shamans: ISFps & ESFps
Paladins: ENFps & ESFjs
Druids: ENTps & ENFjs