In The Adventures of Huckleberry Finn, Huck and Tom, while both mischievous and both full of a desire for adventure, are different in that Huck has a more mature sense of the world, while Tom remains stuck in childhood. These differences stem from their upbringings and are made evident in the later chapters of the novel when Huck is fighting for Jim's freedom, while Tom, who knows Jim has been set free, continues to want to play an adventure game.
Huck grew up poor and physically abused by his father. In Huckleberry Finn, his father kidnaps him and takes him to an island. Huck, instead of thinking this an adventure, fears for his life and comes up with an ingenious plan to fake his own death.
His entire "adventure" in this novel is about him escaping danger and protecting Jim. Huck, unlike Tom, has nothing to return to—no safety net, so to speak. He has no Aunt Polly. He's even condemned himself to hell for helping a runaway slave. He just has his life and Jim's to worry about.
Tom, meanwhile, has a safety net. His adventures end when he wants them to end. He grew up in a nice home with food on his table every night and without fear of physical harm.
These differences in primary characteristics become evident when Aunt Sally keeps Jim prisoner. Huck has shown he'd risk everything to set Jim free, but ends up relying on Tom, who has always been the leader of their adventures. Tom, meanwhile, already knows Jim is free, that Miss Watson set him free when she died, but insists on playing some type of adventure game, including covering him with snakes, spiders, and other critters to make his escape more believable.
It is not an accident that at the end of the novel, while Tom returns to St. Petersburg hoping to have more "adventures" and probably to live out most of his life, Huck decides to start new by moving west.