Thanks for the A2A.
I wish I can choose one but I couldn't, so here are my contenders for this title of best bollywood movie ever. I have selected them based on the sheer impact on history of bollywood and Indian society. Take your pick :)
Released in pre-indepedence era(1943), it remains one of the biggest hits of all time in bollywood. It ran for 187 continuous weeks in Roxy cinema in Kolkata, a record which stood for 32 years only to be broken by Sholay. It made Ashok Kumar the first ever superstar of Bollywood.
Surprisingly bold for its time with Ashok Kumar in an Anti-hero role and pre-marital pregnancy, its song "Door Hato ae Duniya Walon, Hindustan Hamara hai" became a chartbuster. Its lyricist has to go undercover to avoid getting arrested by Britishers on sedition charges. (gives us some perspective on "sedition" in light of recent JNU controversy)
If Bollywood had an IMDB of its own, Sholay will be its "Shawshank Redemption" albeit better than that, because once it became the top movie, it was never replaced by any other movie. It has everything which defines mainstream bollywood cinema. In the words of great Dharam paji, "Is movie mein action hai, emotion hai, drama hai, tragedy hai" (this movie has action, emotions, drama and tragedy).
It is common for bollywood movies to get inspired by hollywood but no other bollywood movie has inspired so many other movies (Karma for instance). Did you know that there is a movie based on , based on the famous character played by Jagdeep in Sholay (but then which Sholay character is not famous :D). Enough said.
Interesting Trivia: Sholay was allegedly a twist on an earlier bollywood classic, do aakhein barah haath apart from being inspired from then prevalent hollywood westerns.
3. Ham Aaapke Hain Koun:
It was such a monster hit that some people watched it 100 times and over (that too in a cinema hall). People travelled from small towns (like mine) to bigger town just to watch this movie.
Such was its impact, that the song charts had its song on tops slots for an entire year. One song of this movie only to be replaced by another song of this movie (remember Superhit Mukabla :)).
Dubbed by critics as a glossy wedding video, it remains the quintessential bollywood feel good movie. Tuffie remains one of the most loved Dog in bollywood history and Renuka Shahane the most loved Bhabhi :)
20 years after DDLJ, there are still girls aspiring in small town india to be the Simran and find a Raj for themselves (how else would you explain the NRI wedding craze :P). This movie ran for 1009 continuous weeks in Maratha Mandir theatre in Mumbai (allegedly YRF paid them), was taken off and have to be continued after the fan uproar. So much so, that watching DDLJ in Maratha Mandir has become the "thing-to-do" for anyone coming new to Mumbai.
DDLJ made SRK the Superstar that he is today, Kajol became frozen in her role as Simran in our consciousness and the last scene Simran runs to catch the train has been watched, rewatched, spoofed, copied so many times that we have lost count (i infact get mildly irritated by its reference these days)
It also started the era of NRI focussed movies (Karan Johar made his entire career out of it).
Very few movies have such a defining impact on bollywood as this one.
P.S.: Some Quorans may find this list a tad plain, because these are movies liked by masses. Nonethelesss I doubt anyone would deny the impact each of these movies had on our Society and bollywood.