Both Caesar and Cassius prove themselves to be shrewd judges of human character. Of these two men, Cassius is perhaps the better judge. Caesar, after all, lets himself be escorted to the Capitol by a group of men who have concealed weapons and intend to assassinate him. If there was any time when Caesar should have used judgment of human character, it was on that morning when all the conspirators called on him at his home. Brutus is a poor judge of human character. He is noble and idealistic and judges others by himself. Antony seems a fairly good judge of human character, as seen by the way he manipulates Brutus and then manipulates the plebeians in his funeral oration. But he does not seem as shrewd as Cassius and Caesar. He is not judgemental. He is hedonistic, careless, capricious, impulsive, temperamental. When Caesar expresses his apprehensions about Cassius, Antony replies:
Fear him not, Caesar; he's not dangerous;
He is a noble Roman and well given. (1.2)
When Antony later becomes co-ruler of the Roman Empire with Octavius, he proves himself incompetent for such a responsibility.
So the choice would be between Caesar and Cassius. Caesar proves to be a shrewd judge of Cassius when he tells Antony in Act 1, Scene 2:
Let me have men about me that are fat,
Sleek-headed men, and such as sleep o' nights:
Yond Cassius has a lean and hungry look;
He thinks too much; such men are dangerous.
Would he were fatter! But I fear him not,
Yet if my name were liable to fear,
I do not know the man I should avoid
So soon as that spare Cassius. He reads much,
He is a great observer, and he looks
Quite through the deeds of men. He loves no plays,
As thou dost, Antony; he hears no music;
Seldom he smiles, and smiles in such a sort
As if he mock'd himself, and scorn'd his spirit
That could be moved to smile at any thing.
Such men as he be never at heart's ease
Whiles they behold a greater than themselves,
And therefore are they very dangerous.
Cassius shows his judgement of human character in his understanding of Caesar's dangerous intentions, in the way Cassius manipulates Brutus as well as many other Romans to join in his conspiracy, in the way he advises killing Antony along with Caesar, in warning Brutus against letting Antony speak at Caesar's funeral, and in his negative reaction to Brutus' decision to fight Antony and Octavius at Philippi. Cassius is always right but always overruled by Brutus, who is usually wrong. It would seem that Cassius is the best judge of the four principal men because Caesar, although he was the leading man of the age, allows himself to be led to his death like a lamb to the slaughter. Caesar is deceived by Brutus, his good friend, among others. He refuses to listen to his wife, who is giving him very good advice when she warns him to stay at home on the Ides or March. He seems to believe that all the men who come to escort him to the Capitol that morning are friends and admirers, that they have as good an opinion of him as he has of himself, when the fact is that they all hate him. The conspirators are all there because the wily Cassius has organized the plot against Caesar. Otherwise, Caesar would have been crowned king that fateful day.