In the past 3 decades (the time that one has followed Hindi cinema), we have seen two clear superstars of our times, viz. Rajesh Khanna and Amitabh Bacchan. There were many other successful stars (Jeetendra, Rishi Kapoor, Vinod Khanna, and what have you) as also there were other good actors (Sanjeev Kumar, Amol Palekar, Naseerudin Shah, etc.), but if the term superstar had to be used, it would have to be for these two gentlemen only. Sure, in current stars, one may also include Shah Rukh Khan in the same genre, but he is still around, so we will restrict this discussion to Rajesh Khanna and Amitabh.
Rajesh Khanna truly ruled the screens during the 70s and had a huge fan following. He had a style and a charisma of his own. He of course, had a lot of successful films behind him.
By now, there is no real denying that Amitabh had become an even bigger superstar, a true legend of our times, and a name beyond comparison.
I would like to draw attention to an additional factor that is a difference between these two stars. And I got this, while listening to music on the radio, daily, and also at parties and at clubs, where popular music is played.
I could see that even today, some of the most popular songs continue to be the ones from the 70s, and especially from the Kishore Kumar – R D Burman combo. And in fact, a very large number of these were featured on Rajesh Khanna. That these songs continue to be popular after so many years, is an indication of their brilliance.
So the point to be made is that a LOT of the success that Rajesh Khanna got, must be owed to this musical genius of R D Burman primarily, and to Kishore Kumar, the voice behind Rajesh Khanna’s songs. How much of a success would RK have been without these songs and music? That is something we will never know.
As against this, the songs from Amitabh’s popular films are not that famous. Sure, when the films were hits, the songs were also hits, but they have not sustained their popularity to the extent that RD-Kishore songs of Rajesh Khanna’s films have done. Which would lead me to conclude that Amitabh’s films stood on Amitabh primarily, while Rajesh Khanna’s films owe a very large part of their success, also to the music.
That Amitabh on the other hand, had Salim-Javed, Prakash Mehra, Manmohan Desai, Yash Chopra, and others writing and directing great roles and characters for him, is another matter..
Random Musings 
I think “Rajesh Khanna Vs Amitabh bachan” comparison cannot be made.
They have to be evaluated independently.
There is no denying that amitabh bachan is popular but Rajesh khanna
is unique.
If You say that RK is popular because of the songs is devoid of analytical sense.
Imagine AB in those songs. Besides AB also had same singers. and the good songs of AB are popular. Like kabhie kabhi
but we are evaluating acting and not songs
The style of RK was sober his personality pleasant.
Influence in society was negative.
Contrast this with AB. His influence was rogue [ not righteousness anger as projected]
And his acting well nothing nuch to speak about . Even if u look at a film llike anand where both are present and RK role is more advantagoeus AB is under the shadow of RK. A good actor despite a shadow role can hold his own but that didi not happen. And not withstanding the afct to do a role that RK did at his peak career.
I dont think AB is any match for RK.
sanjay
i simply love watching ab movies
Rajesh khanna biggest superstar ever Amitabh bacchan also superstar but cant compare with Rajesh Khanna.
Amitabh bacchan cant stand front of Rajesh khanna because Amitabh bacchan is a media made superstar, Rajesh khanna still remain single real original and undisputed superstar no others actors till date called superstar all others actor is cheap entertainer.
1000 of Amitabh Bacchan cant beat one Rajesh Khanna as a superstar