Let's start with what's good about Antonio:
He is sociable, loyal, caring and generous. We know he is social since we first meet him in a social situation with two of his friends, Salarino and Salanio. It is evident from their conversation that they know each other well and share a close relationship, since the two men express concern about Antonio's depressed state. Furthermore, the men seem to have in-depth information about his personal affairs since they easily refer to them. The manner in which they address each other is also evidence of the gentlemanly courtesy and respect they share.
When Salarino and Salanio take their leave, Antonio is joined by Bassanio, Lorenzo, and Gratiano. He is obviously popular. Their conversation follows the same pattern as the previous one. Furthermore, the men jibe about Antonio's condition and he does not take any offense, which indicates a good spirit and a generally positive frame of mind.
We learn about Antonio's loyalty and generosity in his conversation with Bassanio. Even though he knows that he is going to lose the constant presence and companionship of his friend, he is more than prepared to help him. He cares so much about Bassanio that he is prepared to sacrifice this aspect of their relationship to ensure his friend's happiness. Furthermore, his magnanimity is indicated by his unselfish offer to help Bassanio obtain a loan to woo Portia, by offering his name as surety. Additionally, he later agrees to Shylock's harsh terms in granting a loan. He is prepared to sacrifice a pound of his flesh if he should forfeit on the deal (although he doesn't think it possible that he will).
We also learn Antonio is a devout Christian for, as Shylock states, he has only harsh criticism for the Jew committing what he feels is a sin—profiting from usury. It is also evident from his earlier conversations that Antonio is an astute businessman. He has become wealthy from his activities as a merchant. He has been careful enough not to take unnecessary chances by putting all his eggs in one basket—he has spread the risk by using different ships which travel to different destinations.
Antonio's bad qualities are that he is much too harsh, prejudiced, and intolerant toward people who practice other religions, as evidenced by his criticism of Shylock, his activities, and his faith. He has treated him with impunity and kicked him, spat at him, publicly denounced him, and called him a dog. Because of this, he has made the Jew a lifelong enemy. A true Christian, one would suppose, would have loved Shylock anyway, seeing as one Christian principle is "Love thy neighbor."
I was also disappointed by Antonio's seeming hypocrisy. Although he is severely critical of Shylock earning interest, he is prepared to forgo this sentiment so his friend, Bassanio, may benefit. One may argue that this is further proof of his magnanimous nature and that it is a sacrifice on his part. Therefore, the...
question is why could he then not have made alternative arrangements and borrowed from his wealthy Christian friends if he were, indeed, so disgusted by Shylock's greed?
Shylock has some good qualities of his own. He is also an astute businessman and has profited greatly from his activities. He is a devout father who has taken good care of his daughter Jessica, and has, seemingly, raised her as a single parent, for the most part. He is deeply faithful to his religion and displays in-depth knowledge of scripture.
Shylock is, however, obsessed with material possession and is generally seen as greedy. It seems he cares more about his money and his jewels than people, as evidenced by the fact that he condemns his daughter and states that he would prefer his jewels to her and that he would be happy if she were dead and his precious possessions returned.
Shylock is also stubbornly vengeful and spiteful. He is malicious, harsh, and unforgiving. He deems Antonio's disasters and inability to settle the loan as an ideal opportunity to have his revenge. He has no sympathy and disregards others' appeals that he should be merciful and accept Bassanio's offer to repay the loan at double its value. He insists on having it his own way.
It is this recalcitrance that eventually makes Shylock a victim of his own malice, so much so that he loses everything which he holds dear, even his religion.