Like Hamlet, Laertes first suspects Claudius as having a hand in his father's, Polonius', death. Laertes is quick to react with a vengeful spirit. However, he is persuaded by Claudius to hold his temper. Contrary to this, Hamlet is patient and methodical, not nearly as quick to react with vengeance as Laertes. Also, Hamlet is not going to be persuaded by Claudius in any way. The main difference between the reactions of Hamlet and Laertes with respect to the deaths of their fathers is that Laertes responds instinctively and has revenge in mind immediately. Hamlet has revenge in mind but he is so philosophical that he must draw out his plan for revenge and this includes pretending to be mad. In essence, Hamlet's reaction is part of this act. Laertes' reaction is his real, natural emotional reaction.
Fortinbras' father is killed prior to the beginning of the play, but it is in the battle with King Hamlet, Hamlet's father. Fortinbras, like Laertes and Hamlet, restrains his thirst for revenge but his restraint is because of political realities. In the end, this was a wise move as he, with Hamlet's endorsement, is likely to be the next Danish and Norwegian king. It may be the case that Fortinbras is the most apt to be king, falling somewhere in the middle of the spectrum between the (perhaps) too vengeful Laertes and the too philosophical Hamlet.