On level of efficiency? Alright here's how efficiency works:
Overall Kevin Durant is rank 1. Dude is in 50/40/90 club while scoring so highly. I think he's just a monster shooter.
#2 is Lebron James, because he has good shot selection AND he has the super athleticism to take it to the rim and no one can stop him.
#3 is CP3. I think CP3 has the best shot selection ever (to go along with his superior court vision) and he's a great shot taker, but not on the level of Lebron and KD. He scores less points since his position forces him to facilitate/pass, but eh.
#932299 is Kobe who asks for the ball and fires randomly
Melo takes a lot of shots and he's good at working a single defender but I wouldn't say he's totally efficient, there are quite a few not-so-hot nights.