Of the 5 “classic” hindi singers, the biggest fight has always been between Kishore and Rafi. Asha Bhosle growing up in the shadows of Lata Mangeshkar could only ever go as high as Lata (perhaps at times succeeding her). Lata is perhaps the greatest of them all, men and women. Mukesh, Kishore and Rafi don’t stand as far apart as Lata and Asha. Yet, I (and many people I know) put Mukesh on a paddle below the other two, partly due to fact that he’s a bit typecasted.
Mukesh = rona dhona , raj kapooor euphoria songs.

Just like the McCartney- Lennon comparison which has egged on Classic Rock enthusiasts for generations, Rafi vs Kishore battle has been going on, even in the present generation, even though Rafi died, a good 7 years before I (avg age of our generation) was born and Kishore died a few months after my birth. Now coming to the main question, the debate between the two and my view on it. Even though I was a Kishore Kumar enthusiast since the time I can remember done in by his yodeling and the masti in his songs, also coupled by the fact that until quite some back I wasnt proficient in recognizing the different voices of Rafi & Kishore ( I still can hardly distinguish between old Lata & Asha songs, although newer songs are easily identifiable).

It would actually be a sin to downgrade Kishore when compared to Rafi, coz there might not be much of a difference, but if you ask me, my fav male singer in Bollywood, there’s only going to be 1 answer, Mohammed Rafi.

For the starters, a fact which many might not know is, although its Kishore who is associated with Yodeling and is the only Indian in this list http://en.wikipedia.org/wiki/Category:Yodelers, but its Rafi who was the first one to bring  it into bollywood, using it in songs, as early as the early 50s, while Kishore Kumar popularized it almost a decade later.

I have always had a fascination with the songs of 50s, 60s featuring people like Dev Anand, Shammi Kapoor, Joy Mukherjee and people of that generation and while songs from Rajesh Khanna period are huge favourites with people all around, but I have more than often found those songs, either sad (lost of rajesh khanna songs) or Happy go lucky(typical Kishore songs) and I like these kinds of songs, but the soul stirring, the harmoniously beautiful songs which came in the 50s and the happy go lucky  + romantic songs in 60s, are more of a feature of Rafi than Kishore. Kishore Kumar while managing to be succesful in the early decades of his career (he had a proper start to his career in mid 50s) only came to the fore in 70s with songs in the film Aradhana, being the important milestone in his career, but before that it was Rafi all the way.

In my opinion, while Mukesh is chained to sad songs, Kishore is more or less limited to the cheerful and sad songs, but Rafi with his ethereal voice always fits the bill for me, whatever be the type of songs, he has hummed out songs, which would surpass Mukesh anyday, his romantic songs/duets with Lata/Geeta Dutt would always be counted as the most romantic chapter of hindi music, while he couldnt give Kishore a running when it came to the bubbly and ecstatis songs, but perhaps the most famous fast paced song of bollywood, Yahoo! Chahe koi mujhe Junglee kahe, was sung by NOT Kishore but Rafi, which can us a fair idea about his talent.

While I will always be enamoured by Kishore’s voice in songs like Diye Jalte hain, Roop Tera Mastana, Mera Jeevan Kora Kagaz and likes but the only question to my all time listing preferences will always be Rafi because his songs have always  retained that freshness for me 50-60 years after they were recorded, but with Kishore you at times tend to get bored, more so coz of the type of songs he sang, rather than his voice being the reason. But, when you dont have much to chose from, this is the type of things which can make the minor difference.