The most profound and notable difference between Tom and Huck in The Adventures of Huckleberry Finn is their treatment of others. This is evident in their interactions with Tom's Aunt Polly, one another, and especially Jim.
While Huck is generally a very progressive character, and one who does not relish in manipulating others--too simple by half and mostly only concerned with enjoyment and happiness to manage such behavior--Tom is clearly the cleverer and more mischievous of the two. Due to his situation, Huck displays more maturity than Tom, who lies often--and well--and thinks of Jim as a mere slave, rather than as a person.
I would find instances in the text to further support this point, but essentially, Tom is the foil to Huck in terms of character analysis.