Sharingan users are not fast by default (It just so happens that Kakashi, Itachi, and Madara are insanely fast anyway) their strength tends to lie in being able to see every seal formed no matter how fast as long as the jutsu users hands are exposed.
Still, in terms of speed and efficiency, It would have to be Itachi (surprise surprise)
He (according to epsidoe 82 of the original series) formed seals so fast that Kakashi barely noticed (I don't have the episode anymore so can someone verify) and pulled out a hand full of shurikens to distract Kakashi as he launched the jutsu at his feet.
And thats what I base my judgement on.
-End Monologue-