Honestly, Goro. His VA during the confrontation scene was pulled off incredibly well. It's awesome that he goes from sounding so pleasant during most of the game to sounding so downright /venomous/.
I think Akechi's range is excellent and everything serves the character well, but his normal voice is kind of bland to me (which ALSO serves the character but I just don't care for it :<)
P4 was a leap above P3 in terms of voice acting and P5 kinda knocked 'em outta the park.