Wrong. Davros
once posed as the Emperor Dalek. He is not. However, Davros and the Emperor Dalek have never been seen together in the same episode, so the Daleks never actively serve both. But I'm sorry if there's been any confusion. Davros is not the Emperor Dalek, you'll have to trust the man who's been watching Doctor Who since he was two years old. (That's me, by the way.
)
Davros: Creator of the Daleks. Wants to be their supreme controller but is often betrayed by the Daleks, who believe Davros, like all other life in the universe, is inferior. Eventually this led to a schism, creating two Dalek factions, the Imperial Daleks that served Davros and the Renegade Daleks who were on their own. I would imagine that by the new series, the Daleks settled their petty dispute and are now united again.
Emperor Dalek: The Daleks' elected representative, so to speak. The Emperor Dalek was (I believe) created by the Daleks to lead them. Daleks leading Daleks obviously works for them, but Davros leading Daleks doesn't.
I hope this clears things up for you, Ross.