Boromir will always be my true favorite. I find his character much easier to relate too than any other. He is loyal to his friends and people, respected by many, and loves his home and everything he does is with Gondor in mind. And unlike any other member of the fellowship, he was the only one corrupted enough by the ring to act. But in his shame he fought ever harder to protect his friends.
He was also, in my opinion, the key to Aragorn finally accepting his heritage. Even Elrond and Arwen could not convince Aragorn to think about reclaiming the throne. But Boromir, being so sure of his own purpose, was confused why his countryman, and rightful king, was so unsure of his path. I think that angered Boromir and was the cause of many disagreements. But his death was ultimately the cause of Aragorn promising him to protect their home.