In no particular order:
1) Shinsekai Yori
2) Shinsekai Yori
3) Shinsekai Yori
4) Shinsekai Yori
5) Shinsekai Yori
Honorable mentions go to Fate/Zero, Psycho-Pass, and Madoka, so basically just give them all to Gen
Dunno how much of that is just half-joking, but that's pretty much my opinion on the matter. He played better in TWOWS and Inception, in part because there wasn't much to play except grunting, eating fish, and being filmed in the cold in this role.
Confession: The only time I've ever used the car horn was at the start of my first driver license test when the examiner was telling me to turn on turn/brake lights and the horn to make sure everything worked.