Biff is the preferred son, valued above Happy, given support and confidence from his parents. Happy is clearly not approved of and there is little hope that he will amount to anything.
These differences help to inform the characters of the brothers.
Their relationship to Willy may be the most significant relationship for both brothers, affecting Biff and Happy in ways that make them similar and different.
Biff and Happy share their father's tendency to concoct grand schemes for themselves and think of themselves as superior to others without any real evidence that the schemes will work or that they are, indeed, superior.
Biff eventually changes his relationship to Willy and to the fantasies that Willy insists on maintaining. By turning his criticism on himself, Biff realizes that he is responsible for himself, for this failures, his successes (potential successes), and his nature.
Happy never makes this change. He skips out the bill at dinner, leaving his father to pay and demonstrating a tendency (like Willy's) to simply deny reality in preference to a pleasant fantasy.
While Happy remains glued to a fantasy, Biff comes to a realization of a highly personal reality.
"We’ve been talking in a dream for fifteen years. I was a shipping clerk."
Biff makes this change. Happy remains convinced that he is special; bound for great things.
Happy over-compensates for insecurity and self-esteem issues, trying to gain what affection he can from Willy and Linda. He is not strong enough to face the truth of his character. In this way he resembles his father.
In the speeches the brothers give at Willy's funeral, we see the differences between the brother's clearly. Biff says that Willy never knew who he was. Happy says that Willy had the greatest dream there is and promises to continue pursuing that dream on his father's behalf.
Biff and Happy are willy's sons. Biff has always been favored by Willy as a young man with enormous potential in life. Both are dreamer. Both are the representative of the young generation. Both of them are not contended with their life. Girls were mad after Biff and even Happy. The two brothers always feel loneliness. Happy suffers from a kind of existential boredom while Biff feels suffocation in the mad world. Biff has a moral sense, a prick of conscience but Happy has none
When we look at Biff we find his failure in life is a terrible illustration of the tremendous waste of human resources in a world of maddening competition. The only promising feature in his life has been his sportsmanship. In other ways he has been a great disappointment. He has been tramping around for a number of years without settling down to a meaningful existence. According to Linda he needs an understanding of the self, a discovery of the self. His acute malady is his 'lostness'.
Biff is less assured than his brother, succeeded less and his dreams are stronger and less acceptable than Happy. At one time girls were mad after him and psid for him but now the old humour, the od confidence is gone. He is now a mere shadow of his former self.
On the other hand he seems to be a sensitive boy who can well diagnose the cause of his failure of disintegration. But he is a mistrained person, unfit for the maddening world of competition for the rough and tumble of the daily routine. Even the beauteous natural scenes and sights have lost their appeals to him and he says that he has come home to waste his time.
One of the reasons of his failure is that he was not "brought up to grub for money". He does not know how to do it. His strong feeling is that it is almost useless to accumulate wealth all one's life and then not to have peace of mind to enjoy it.
Another reason of Biff's failure in life is that Willy showered excessive fondness on him even to the limit of spoiling his career.
The turning point in his life was the incident at the Boston hotel. Before that he worshiped his father but now the sentiment changed
HAPPY, on the other hand, is also a tall well built young man. "Sexuality is like a visible color on him or a scent that many women have discovered, he is also lost like his brother but in a different way. For, he has never turned his face towards defeat and thus is more confused and hard skinned, although seemingly more content". Though he is a dreamer like Biff yet more assured. In his sex appeal, he seems to be a Don Joan.
Happy is making money but he is emotionally drained and extremely perturbed by a haunting sense of loneliness. He sufferr from a kind of existential boredom. He admits that money and sex have failed to provide him relief. Sex is his greatest weakness. This nature prevents him from marrying.
He also wants to please his father at any cost, even telling a lie. Happy can be summed up as a trickster and a deceitful person.