Mohammad Rafi is one of the legend in Indian Music Institution.
The best song of Rafi I like is "O Duniya ke rakhwale(Baiju Bawara)". He was the voice of Bharat Bhushan. He performed playfully for Shammi Kapoor, Rajinder Kumar (Aje hamse bach kar-Arzoo.). The dard of his voice-no one can ever sing like that. He has a mature simplicity in his voice.
Other songs I like are " Door rehkar na karo baat, Tere mere Sapne, Bahaaron Phoool Barsao, Jab bhi ye dil udaas hota hai, Kar chale hum fida, Ae wata, Ab kya misaal, Ehsan tera, sau baar janam lenge, do sitaron ka, hui shaam unka, pardesiyon se, kaun hai jo sapnon me aaya ". The list is long so that’s what I can say.
He sang for India, he sang for humanity. He left us in eighties. I have seen many competitors in realty shows trying to imitate him but I am sure no one can, ever.