I really don't want to go into it because I'm pretty sure this debate was going on when I last posted here more than a few years ago.
Some simple bits of information for people, no names mentioned but I'm looking at you Slick when I say this. Still, no names ha
Great India is right, it is unfair to compare batsmen across eras. However where Bradman earns the right to be considered all alone, where he is the benchmark by which all future batsmen are measured is the staggering difference between him and his contemporaries. If other players of the Dons time had been averaging in the 70's and 80's then it would be acceptable to attempt to claim his average of 99 as belonging to a different era. They did not. Sachin is the best of his era because he has proved himself to be that bit better than the other great batsmen of his time. Bradman not only proved himself to be the best of his generation, but did so by such a margin that no other player has ever demonstrated such a gap in quality and ability in relation to his fellow players.
For that reason, Bradman sits alone atop Mount Olympus, leaving Zeus to throw his lightning bolts at Sachin, Viv and all the other greats of their time.