One could argue that the main difference between Biff and Happy Loman concerns the fact that Biff ends up acknowledging that he has led a superficial, unsuccessful life and has wasted most of his years chasing a futile dream while Happy remains delusional and out of touch with reality following Willy's death. Towards the end of the play, Biff recognizes that he has lied to himself for the majority of his life and has unfortunately subscribed to the American Dream like his father. Instead of focusing on his inherent happiness and attempting to find an occupation that suits his interests and abilities, Biff was continually sidetracked by the importance of attaining wealth and pleasing his unrealistic father. It is only after meeting with Bill Oliver that Biff becomes determined to discover the truth about himself and break the cycle of lies in his family.

Unlike Biff, Happy continues to subscribe to his father's false realities and refuses to seriously analyze his life. Happy seems content living a delusional, immoral life and significantly exaggerates details about his career to overcompensate for his feelings of inadequacy and lack of success. Happy rejects Biff's opinion that they are failures and takes pride in pursuing affairs with many women. Overall, Biff matures throughout the play and experiences a dramatic transformation by embracing the truth about his family while Happy continues to accept lies and blatant exaggerations.

As the play opens, the obvious main difference between Hap and Biff Loman is that Hap remained in his hometown after high school while Biff left the state. Hap has worked steadily in the same store, hoping for a promotion, and sees his parents often. Biff has tried "twenty or thirty different kinds of jobs" in multiple states. Hap comments that Biff's old self-confidence is gone, while the stage instructions explain that Hap is "hard-skinned" and hasn't allowed himself to face defeat yet.

As the play progresses, it becomes clear that Hap is in denial to a much greater degree than Biff is. Biff becomes more and more aware of the truth about himself and his family as the drama unfolds, while Hap remains confused. Hap keeps Biff from confronting Willy and defends his father, telling Biff not to call him crazy. He tries to appease Willy and make peace between his brother and father, and he advises Biff to lie to Willy about the failed appointment with Bill Oliver just so Willy will be happy for a while. By the end of the play, Biff is tired of lies and playing games. He tells his father the truth about Bill Oliver and about his own failures, including the time he spent in jail. During that conversation, Hap remains in denial. When Biff says, "We never told the truth for ten minutes in this house!" Hap responds, "We always told the truth!"

In the Requiem, Hap still defends his father. Biff says Willy had the wrong dreams, but Hap, becoming antagonistic toward his brother, retorts, "Don't say that!" Hap digs in his heels, following the "good dream" of his father, but Biff is able to say, "I know who I am, kid."

The main difference between the two brothers is that Hap is content to remain in denial and is a static character. As a dynamic character, Biff has a revelation about who he is and can finally look at his own faults objectively.

The biggest difference between the Loman brothers is that Biff once had a sense of purpose in life. Once upon a time, he was headed for great things; it was almost a given that he would go to school on a football scholarship. The world was very much his oyster, and there was every indication that he'd fulfill his father's dreams. But thanks to Willy's unrealistic expectations—not to mention the illicit affair he conducted with a secretary—Biff went completely off the rails, and now he's going nowhere in life.

Contrast that with Happy. He's never really had any sense of purpose. He's breezed through life without any definite plan. At times, he seems much more concerned with chasing women than with putting in the hard work necessary to be a success. Despite this attitude, he still clings to his father's delusional hope that all you need to be successful in life is to be a well-liked man. Like Dickens's Mr. Micawber, he assumes that something good will eventually turn up just around the corner.

The main difference between the characters of Biff and Happy Loman is that, in the end, Biff gets to realize that his life has been a lie. Although Happy is aware of the same situation, he continues to follow his father's steps and keeps denying that anything is wrong with the Loman family. However, Biff explains the situation best when he says:

"I realized what a ridiculous lie my whole life has been."

As a result of this discovery, Biff decides to change the vicious cycle that the Lomans live of denying reality, confronts his father about it, and chooses to leave the Loman household for good.

Meanwhile, Happy gives due justice to his nickname. He is the "OK" man. Everything is fine with him, even if its under denial. He tries to dissuade Biff each time Biff discovers that something is just not right in the way the Lomans act. That is, perhaps, because he is used to living under the shadow of Biff and does not know how else to proceed in life. Eventually, however, he falls under the Loman spell and tries to follow Willy's sales dream. Therefore, Happy perpetuates the cycle that Biff is trying to eliminate.

Yet, prior to Biff's epiphany the brothers were inseparable in their combined co-dependence of each other. They were clueless, immature, enmeshed, and unable to act like responsible adults. They were both psychologically castrated by the overshadowing past of Willy's control over them. They used to be lost children, basically, until finally Biff grows up and cuts loose. This is how they are very different, but used to be very much alike at one point.