In Willy's eyes, both Bernard and his father Charley share the same flaw of being unattractive and uncharismatic. Willy values these qualities over hard work and intelligence, which is why he admires his own son, Biff, who he sees as embodying these traits.
Willy contrasts Biff to Charley's son, Bernard, whom he sees as being too bookish and unimpressive. He believes that Biff's good looks and athletic ability will be enough to carry him to success, whereas Bernard's intelligence and hard work will not be enough on their own. Willy's vision of success is based on superficial qualities rather than substance, which is why he values Biff's charm and charisma over Bernard's intelligence and diligence.