In Shakespeare's Hamlet, Fortinbras and Laertes serve as foils to Hamlet. They present alternative ways of handling the same situation that Hamlet is in. They suffer the loss of their fathers, as Hamlet does.
Fortibras sets out to attack Denmark to avenge the death of his father in battle against Denmark, but is stopped by his uncle, who is now king of Norway.
Laertes storms in to Elsinore intent on killing Claudius, who he thinks had a part in the death of his father, Polonius.
Neither of these alternatives are necessarily better, they are just alternatives. Laertes, in particular, is hot headed and dishonorable. He allows himself to be manipulated by the king and hatches a plan to poison Hamlet.
And Hamlet does more than just sit around and worry. His character is considered to be one of the great thinkers of English literature. And there are numerous possibilities that might cause him to delay his revenge: he is unsure of the Ghost's identity for the first half of the play; he is suffering from depression and maybe madness; it is not a small thing to kill a king; he doesn't want to send Claudius to heaven by killing him while he is confessing his sins, etc.
But, for better or worse, Fortinbras and Laertes do serve as foils to Hamlet.
All three men try to take revenge for fathers murdered, but each are delayed in doing so, and each regret the act after:
Fortinbras takes political action to avenge his father's death. Old Fortinbras was killed by Hamlet Sr., and Hamlet Sr. was already killed by Claudius, so Fortinbras decides to wage war on the entire state of Denmark. He tries to be a man of action, but he is called back by his uncle, the sick king of Norway. So, he wages war on Poland instead. In the end, when he reaches Denmark all are dead, and though his invasion is bloodless, he never really enacts personal revenge. He is the only avenger standing, a lonely enterprise.
Laertes tries to take quick and personal revenge for his father's murder, first on Claudius. Claudius advises that he wait and kill Hamlet during a rigged fencing match. After he is stabbed, he regrets his role as avenger because he has been used as a tool for Claudius' revenge. In the end, quick personal revenge causes one to be manipulated.
Hamlet is caught between revenge and mercy, mainly because of fear of damnation and problems with his mother. His father mandates revenge, though Hamlet is unprepared to do so. He delays revenge because of fear and supernatural misgivings: how to send Claudius to hell and his father and himself to heaven (is it even possible?). In the end, he enacts revenge on Claudius, but it comes after he is killed. He has lost everything: mother, girlfriend, and his own life.
To me, the major similarity between these three young men is that each of these men feels (at some point in the play) that his family has been wronged and he needs to take revenge. Hamlet, of course, has had his dad killed. Fortinbras's father was killed too, and part of his kingdom taken. For Laertes, the wrong is later in the play, but his dad has been killed too.
What's different about them, to me, is that Laertes and Fortinbras are confident men of action. They act quickly to take revenge. Hamlet, on the other hand, is famous for sitting around worrying about what he should do instead of actually doing something.