To answer that question, we need to ask another question. What do you mean by a leader. A leader is someone who has a significant mass following and people do as he / she asks them to do. Who leads by example and has made a significant contribution towards shaping the country. Following these tests, we have identified the top 5 which to our mind should come in this list. Giving chronologically from the time they were active:-
- Netaji Subhash Chandra Bose: -
Who: - Freedom fighter par excellence; Defeated Gandhiji's candidate in the NCP elections; Managed to slip past the British intelligence and made way to Germany; Met Hitler who was a world leader; Formed alliance with the Japanese; freed the Indian POW's and formed the Azad Hind Fauz. 

Why: He is in this list because he managed to do what was unthinkable at the time. Escape from a well guarded home prison under British watch. Going undetected to Germany. Meeting Hitler who was at the peak of his power and a world leader at that time. Convincing Japan on the need to free Indian prisoners of war and forming the Azad Hind Fauz with them. The very idea. The very audacity in execution: that was the brilliance of Subhash Chandra Bose. He still ignites popular imagination and is still relevant enough to be discussed at social events(specially on the mystery surrounding his death). He defied the formidable force of Mahatma Gandhi and won the elections to the President of Indian National Congress against the candidate suggested by the Mahatma.
2. Sardar Vallabh Bhai Patel
Who: A leader who through his actions came to be known as "The Iron Man of India.".
Why: He is in this list because he did what others in his time failed to do. He recognized the problems which the fleeting millions faced when they escaped from the fires of partition. He organized camps for the refugees. His efforts resulted
in consolidation into what is now known as India. As per the understanding between the British and the princely states, the princely states had t
he option to join India; join Pakistan or to remain independent. It was Patel who managed to coax, coerce and push the states to join the Indian State. Some states like Sikkim were left which later merged with India in the 1970's. Patel has been credited at giving shape to what is currently India.

he option to join India; join Pakistan or to remain independent. It was Patel who managed to coax, coerce and push the states to join the Indian State. Some states like Sikkim were left which later merged with India in the 1970's. Patel has been credited at giving shape to what is currently India.
3. Indira Gandhi
Who: Daughter of first prime minister, Jawahar Lal Nehru, Indira was to India what Thatcher was to UK. She was tough, determined and followed.
Why: At the peak of her career there was a saying: India is Indira and Indira is India. If she does not deserve to be here, none do. She won for us the 1971 Indo-Pak war which resulted in an independent state called Bangladesh. Her autocratic ways were criticized by many even as she went ahead, confident in herself, in her set ways. She took many bold decisions and not all of them correct. Declaring national emergency w
as one such case. She led a volatile life, often disregarding populist moves for what she considered right. Rebellious powers grew as a result of this and ultimately costed her her life. Her don't care a damn attitude, her persona and charisma, her defiance of the US which was protecting Pakistan, her defiance of the popular choices when she declared emergency and her defiance of the sacred rules in operation blue star is what makes her a fit entry to this list. She was, modern India's fieriest leader.

4. JP
Who: Jaya Prakash Narayan or JP was the Lok Nayak (People's hero).
Why: Because of his revolution against Indira Gandhi (total revolution); because he was the main cause for her declaring national emergency; because he was instr
umental in igniting the popular imagination and doing all that was quite un-doable at the time. He brought to the fore what was known all through but never spoken: the trap of corruption and the hunger which India had fallen into. He spoke the people's language - in his own words. And that is what endeared him to the people. They saw in him their own face, their own suffering and their own voice. They banked upon him. They voiced his voice and they moved as per his direction. This is what a leader is all about.

5. Narendra Modi
Who: The 15th Prime Minister of India and a world leader.
Why: Because in 22 months he has achieved which few have achieved in 2 decades. Because his vision and mission inspires not only the Indian ps
yche but also the world community at large. Under his leadership, the world listens. Because his ministers are working (which is a first in the Indian political scenario):

a. Suresh Prabhu has literally put life onto the sleeping Indian Railways. With major trains having wifi and coaches being clean. No major accidents since he has taken charge. Moreover, he listens. One tweet and help is on the way. One feedback and response is immediate. That is, putting the railways back on track.
b. Sushma Swaraj being external minister has ensured citizens can connect via twitter. One tweet with hashtag sos and help will arrive. She has spearheaded the Iraq evacuation where 168 Indians were saved. Gen VK Singh has helped and personally supervised the Yemen evacuation.
c. With defense being in the hands of Manohar Parrikar we have managed to get inside Burma for eliminating terrorists. A first for us.
Because there has been no major terrorist attack since Modi has assumed office (Pathankot notwithstanding) , because India is emerging and being recognized as a world leader.
And finally, because wherever he goes, the Modi chant follows - be it within or outside India. If that is not being a great leader, what is.
So, why does the list not contain Mahatma Gandhi & Pt. Nehru? Well....Mahatma Gandhi was an icon. He was not a leader but a saint who also did politics. He was Mahatma. This list is not about saints. Pandit Nehru was a dynamic personality. Lot of critisim about him on how he operated and dealt with - but his persona was overshadowed by the likes and presence of Gandhi, Bose, Azad, Patel and others. While the others in the list, stood their own grounds on what they did. Yes, Nehru was the first PM. But being the first there was so much less competition. He does deserve to be on the top 10 but I could not remove anyone from the existing list for his inclusion.