This is an interesting question and allows one to map out some of the patterns in this complex play. Fortinbras, Hamlet, and Laertes seem to occupy three corners of the options for young men of court. Each loses his father, and each has reason to seek revenge. How they go about seeking revenge tells us about them not just as characters but also as intellectual or political options.
With Fortinbras, we seem to have an older version of the Germanic hero, occupied by questions of honor: his father was killed and his land was lost; he will fight to restore that land. In act 4, scene 4, Hamlet sees him crossing to battle for a piece of land of little worth:
Witness this army of such mass and chargeLed by a delicate and tender prince,Whose spirit with divine ambition puff'dMakes mouths at the invisible event,Exposing what is mortal and unsureTo all that fortune, death and danger dare,Even for an egg-shell. Rightly to be greatIs not to stir without great argument,But greatly to find quarrel in a strawWhen honour's at the stake.
Fortinbras's honor and his willingness to defend it, seemingly without thought or reflection, end in him gaining Denmark's crown. We can even look at this play as the comedy of Fortinbras—yet he is a man who lacks all the brilliant consciousness and self-awareness Hamlet demonstrates. He is a man of revenge, of action, and of blissful sanity. It is hard to imagine Fortinbras having any thought deep or complex enough to drive him mad.
Laertes is a more modern man. Like his father, he speaks in polished truisms taken from commonplace books. He seems to follow his father's advice to turn himself into a socially acceptable ornament, offending no one and standing for nothing. When his father and sister die, he feels bound by duty to seek redress, and he is willing to take the Machiavellian way to it. Before he left Paris for Denmark, he prepared himself for subtle revenge:
I bought an unction of a mountebank,So mortal that, but dip a knife in it,Where it draws blood no cataplasm so rare,Collected from all simples that have virtueUnder the moon, can save the thing from death
He has cause for grief and revenge, but something in his character makes his actions feel more performative than deeply felt. This is also why Hamlet jumps into Ophelia's grave, offended at Laertes' seemingly artificial forms of grief. Laertes may seem mad with grief at various moments, but he easily slides back into conventional behavior when he sees an opportunity to serve his purpose.
Hamlet, by contrast, resists the advice his mother and uncle offer early in the play, fails to follow his duty to office and family, delays acting on his grief and his duty as the son of a murdered father, and perhaps even gives in to his "antic disposition." Yet Hamlet is the character who, despite his many failures to perform his duty, to "take action in a sea of troubles," and even to channel his thoughts into a linear path, commands our awe and terror.