So I googled "best defender in history" to read some lists, I like lists.
Nesta is so criminally underrated by non Milan fans. I was shocked.
Nesta is the best CB in history of football.
The funny thing is most of those lists say Ferdinand, Vidic, and Cannavaro were better than him
Nesta was THE BEST of his generation. The only reason he didn't perform well for the Italian NT were injuries. In 2006 he outperformed Cannavaro vs. Ghana and USA before he went down against Czech Republic. I have no doubt had he stayed injury free; he would have deserved the Balon d'Or over Cannavaro.
Now for being the best CB of all time I think Nesta is a rank below Baresi and Beckenbauer respectively. Nesta is not as good defensively as Baresi and not as good an organizer and distributor as Beckenbauer.
The title of best CB ever comes down to preferences just like the Pele/Maradona debate and I pick Baresi. Baresi was a brilliant leader, one of the best readers of the game, and in his prime he was untouchable when it comes to defense. Not even Gaetano Scirea comes close to him in defending. On the other hand, Beckenbauer is really overrated when it comes to defense because people make it seem as if he was some superhuman who was impeccable in defending AND attacking. Beckenbauer was better in attacking but not Baresi's equal when it comes to defending. Plus we see how great of a leader/teacher Franco was thanks to Maldini
Sorry for the long response I just thought it was an interesting subject.