This is the right one.

In my opinion, though some of the others have a similarly superb grasp on his character and mannerisms, this one nails his cadence, and frankly how much like a "typical adult" he should sound compared to some of the more obviously youthful auditions. Kosaku kind of peters in and out of being as smug as I'd like, though. I'd have auditioned myself if I weren't a tiny baby boy unable to sound like an un-exaggerated 30 year old man, considering I've studied Kira harder than anything academic, but this is my pick of the existing auditions.