As a disclaimer, you need to understand what you are asking is a subjective question. The answer that you receive is, therefore, going to be a subjective one as well. What this means is that the answer is one based upon a personal interpretation of the play and the characters of both Shylock and Antonio.
That being said, in the play "The Merchant of Venice", one could reasonably support the belief that Shylock sins, but the more thought provoking question is: does he sin more than Antonio.
Antonio borrowed the money from Shylock based on un-payable terms. Once the debt comes due, and Shylock is offered six times the amount of the debt, he refuses and desires to hold Antonio to the original bond alone- Antonio did not have the money by the date promised and, therefore, owes Shylock a pound of flesh.
Shylock admits that he does not like Antonio. By stating this, Shylock breaks one of the Ten Commandments: Love thy neighbor. Not only does he sin in this fashion, Shylock knows that the taking of the flesh will physically harm Antonio. Shylock has no concern for this either.
While both men are prejudice against the other based upon religious beliefs (Shylock is Jewish and Antonio is Christian), it does not change the fact that both sin.
The most important part of this conundrum is that, according to most religions, sin is sin. Therefore, one cannot be 'more' of a sinner than another. Once one commits a sin, that person is a sinner. It, by God's law, does not matter if one commits one sin or a thousand- that man (or woman) is still a sinner.