well u cant really compare them
atif is kinda pop and soft rock. 1st album was the best. second was OK and the third one is just ok. Bad videos, not a single video out there that i could praise. Atif suck big time when singing live and his styling sense is awful.
Ali zafar is melodious movies style singer. He has great voice, heaps better than Atif. He can paint, act and model. His videos are one of the best and his styling and dressing sense is just gr8. 
and he has been rated as one of asia’s ten sexiest men.
adding to that I love Atif songs. I believe if he gets out of his brothers nest he can do better.