The Prince chooses the gold casket for several reasons.
The Prince is quite conceited and when he reads the inscription on the lead casket:
'Who chooseth me must give and hazard all he hath.'
He believes that he is a 'golden mind' who would not stoop to hazard all he has for such a worthless substance. It is beneath him.
The inscription on the silver casket reads:
'Who chooseth me shall get as much as he deserves.'
The Prince assumes that he deserves Portia since they are equals in birth and fortune, in graces and breeding. He however feels that he deserves more than just to be an equal in those aspects, he also deserves to be loved. He then turns his attention to the gold casket on which the inscription says:
'Who chooseth me shall gain what many men desire.'
The Prince concedes that the inscription is true - all men desire the fair and prosperous Portia and therefore come from all corners of the world in an attempt to win her hand. He uses beautiful metaphoric language to describe from whence every man comes to chance their luck at winning the hand of Portia whom he describes as an earthly saint. These men cross vast, empty deserts as if they were nothing, they take on the oceans as if they were mere rivulets - all to win Portia's hand.
The Prince reconsiders the other two options: first, the lead casket. He believes that lead is too base a metal to be associated with Portia. It is an insult to even contemplate such a thing. The mere thought of her being buried in a casket made of such a worthless substance is an ignominy.
Second, the silver casket is not worthy of Portia's stature. Its value is ten times less than gold. He compares the casket to an English gold coin which has the image of an angel stamped upon it, but that is a mere image. Within the casket lies something of greater value - an angel in a golden bed (Portia).
The Prince therefore dismisses the other two caskets and chooses the gold one. He is greatly dismayed when he opens the container and finds a skull with a scroll inserted into one of the empty eye sockets. He reads the scroll which states: 'All that glitters is not gold ..' The prince had been deceived by the allure of what he believed to be the most precious of the three choices. The scroll teaches a lesson:
Many a man his life hath sold
But my outside to behold:
Gilded tombs do worms enfold.
Had you been as wise as bold,
Young in limbs, in judgment old,
Your answer had not been inscroll'd:
Fare you well; your suit is cold.
The prince should have used wisdom and the judgment of an older person instead of just his courage and youthful exuberance when he made his choice. The prince, obviously disappointed and deflated, does not tarry and leaves immediately.
The Prince of Morroco being one of the suitors of Portia came to try his luck on winning her. As mentioned in the drama the Prince has to select one of the 3 caskets available. Gold, silver and lead respectively. The Prince approached the Gold casket which read " Who chooseth me shall gain what many men desire.',
His reasons for selecting this was the lead casket approached a threat to the selecter and he was not bold enough to select it, although he praises himself in front of Portia. 'Who chooseth me must give and hazard all he hath.' he also thinks that the lead casket is not worth to hold Portia's picture.
Since the silver read 'Who chooseth me shall get as much as he deserves.' he thinks that he is equal to Portia in terms of birth and money. however he also thought that he is above portia. thus he moves on to
the gold casket. He thinks this correct, as Portia is thing that everyone in the world wants. Thus he selects the gold Casket.