I guess, Hannibal is the greatest between this 4 generals. Because his victory at Cannae was THE FIRST example of tactical encirclement, this is studying even now by military students. And what did Alexander, Caesar or Pyrrhus give to history? Pyrrhus - saying, Alexander - just an example of what can ambitious young man with great father's army do. Caesar - another example of ambitious and talanted, but governor after all. Btw; Pyrrhus and Caesar were Alexander's fans, and just tried to repeat his glorious way, while Hannibal was going by his own.