Ice Cube's N.W.A. diss "No Vaseline" is generally considered one of the greatest diss tracks of all time. 

Eminem recently ranked it the 7th best ever. In an interview with Rap Genius, Ice Cube spoke on the virtues of the track. (It was like "a bowling ball", he said of the diss against his former group and their manager.) Then he listed some other great diss tracks.

“Some of my favorites is the original ‘Rock The Bells,’ ‘Let’s Go’ with LL and Kool Moe Dee,” he says. “‘Let’s Go’ is crazy, too. ‘Jack The Ripper,’ great record. Then you got disses like Nas and Jay [‘Ether’ and ‘Takeover’], that’s just crazy. Tupac, Biggie going back at it. [2Pac's] ‘Hit Em Up’ was crazy.”

What do you think? Jump to the 23:30 mark to hear Cube speak on diss tracks. During the discussion, he disagrees with Pusha T that there are no rules to disses, stating that when you start bringing up things like family, you've gone too far.