Amit sang two romantic songs. He sounded the same in both, though he did a fantastic job.
Emon sang two different type of songs and sounded different in both. He was more versatile. And if Emon sounded like Sonu in the first song, I think that's a job well done. Because the song cannot be sung in any other way other then the way Sonu sang the song. It is not enough to sound like Sonu in this song, you have get the emotions right and noone seems to find that missing. So according to me, he did a great job.
I am not saying Emon was bad, he was good. But to me Kal ho na ho was not one of his best performances.