Do you agree that Shakespeare is careful to balance the characters of Shylock and Antonio so that we do not feel more sympathy for one over the other?
Shakespeare gives Antonio a decidedly unsavory side to his character while showing the persecution that Shylock justly feels a reaction to, so it is possible, from one perspective, to read The Merchant of Venice with very little sympathy for Antonio and much for Shylock. Granted, Shylock, takes extreme measures in writing up his loan contract but Antonio displays extreme arrogance in cavalierly agreeing to it even though Bassanio has the sense to protest it.
Shylock accuses Antonio of unchristian and uncivil, truly deplorable behavior, which Antonio not only doesn't deny, but claims he'll commit again, and worse, if given the chance. In the opening scene Antonio tells his friends that he is not gloomy about finances because he is not dependent on the success or failure of his present shipping venture. Yet, a few moments later, he tells Bessanio that he has nothing with which to provide him a loan, thus forcing the conflict of the play caused by an appeal to Shylock for a loan. One reading of Antonio's words recognizes that he lies to his friends about his finances and then is forced to confess the truth to Bassanio.
Sympathy for Shylock and Antonio? Yes. We have seen various arguments either way, therefore to resolve the issue is to follow Shakespeare's "instructions"(see Samuel Johnson's intro), that is we are invited to compare MV and ROM every step of the way. We then find Antonio and Shylock's passion identified with Romeo's(for example, the first appearance of Antonio and Romeo involves "sadness"). Antonio and Shylock are sad because Leah is gone, or this hypothesis is "the leader of the band" if I may borrow from S. T. Coleridge. The fact that Q2 of ROM was published a year before MV is one indication that without ROM, MV would not exist.