Okay, I'm going to step in right here. I agree with Namikaze in that Itachi was a prodigy in mastering the Shringan. But Kakashi is more prodigal in general. Kakashi graduated from the ninja academy at age 5 while Itachi graduated at age 7. Kakashi also became a chunin a year after he graduated, meaning at age 6. Itachi, however, took 3 years, becoming a chunin at age 10. Also, Kakashi was a jounin by age 13, while Itachi was ANBU at age 13.
Adding on to this. Itachi mastered the sharingan at age 8 while Kakashi only got it when he turned 13. Meaning, Kakashi made it from Academy at 5, Chunin at 6, Jounin at 13, without the sharingan. While Itachi had it from age 8 on which is probably why he became a chunin and eventually ANBU.
Itachi was very much a prodigy, but you have to admit, Kakashi was amazing to have gotten so far without it, and became even more amazing with it. Had Kakashi been actually born into the Uchiha clan, he would have surpassed Itachi. So in my book, Kakashi is more of a prodigy than Itachi, even though they are both very prodigal.