This is how I look at it. The sorcerer would be the one out in the open flaunting her/his power and daring her/his enemy to challenge her/him. An assassin would play the enemies friend, and slip in and destroy them when they least expect it. They are the deceivers. The nightmare you never see coming until it's too late. They would rule very effectively as know one could predict them. Are they my ally? Are they my enemy, and if so, when are they going to make their move and attack.
I would fear the assassin more than the sorcerer. The sorcerer I at least see coming...
Which focusses more on unlimited power?