I simply went with who both Scipio and Hannibal said was the greatest:
www.livius.org
[10]" It is said that at one of their meetings in the gymnasium Scipio and Hannibal had a conversation on the subject of generalship, in the presence of a number of bystanders, and that Scipio asked Hannibal whom he considered the greatest general, to which the latter replied, "
Alexander of
Macedonia."
To this Scipio assented since he also yielded the first place to Alexander. Then he asked Hannibal whom he placed next, and he replied, "
Pyrrhus of Epirus," because he considered boldness the first qualification of a general; "for it would not be possible," he said, "to find two kings more enterprising than these."