Completely agree with reidalot on this one. Just consider the other options we are given - Bassanio, who obviously uses and manipulates his best friend (and perhaps former lover) Antonio to pay off his debts for his foppery and waste. Antonio himself seems to attach his status and position on his wealth. Shylock is obviously a miserly, greedy Jew, completely fitting the stereotype on this front. Thus Portia, in her willingness to use wealth for the good of others and dispense of it at will offers a completely different approach to money and wealth that is refreshingly novel.
In many ways, this is an opinion question, depending upon your sympathy towards the character's motivations concerning money. However, I would definitely have to say Portia. Her father, to safeguard the family fortune and ensure she marries the best man, makes her inheritance and marriage depend upon the suitor who chooses the lead casket, rather than the gold or silver. When Bassanio chooses the lead casket she proclaims, "Myself, and what is mine, to you and yours is now converted" (Act 3, Scene 2). Portia willingly gives up all, according to her father's wishes, and for love! She gives Bassanio a ring that if he would lose or give away would "presage the ruin of your love." Portia, in her wisdom, does not place money first, as Shylock over his daughter, or Jessica when she recklessly spends the money she stole from her father, or Antonio who willingly bonds a pound of flesh for Bassanio who still owes him money, or Bassanio, who borrows and never repays loans. Portia is even willing to repay Antonio's loan to Shylock because he is her husband's friend. Again, she is motivated by truth and love. The bigger question here may be whether or not Bassanio deserves Portia's love!