Similarities: They are both dependent on each other's friendship and support throughout the novel. They both value each other's strenghts (Gene - intellectualism; Finny - athleticism). Finally, Gene and Finny are both very competitive with each other.
Differences: Gene is rather reserved and shy while Finny is very outgoing and charismatic. Finny has an optimistic attitude about life while Gene is more pessimistic and lets things "get to him". Finally, Finny is secure in who he is while Gene is not and instead, strives to find his identity or peace by "becoming" Finny.
Differences: Gene is more scholarly (Gene is near the top of his class, Phineas average in his studies) , Finny is (Phineas) the better athlete, Finny is more self-confident (able to step outside convention and challenge authority)
Similarities: there are not a great deal of similiarties between the two teenagers. A similarity lies only in the fact that Gene assumes that his "friend" is as envious of his scholarly abilities as much as he is envious of Finny's athletic prowess. Of course, they have their ages and school in common, too. But Gene is severly lacking in self confidence and maturity. Finny may lack maturity as well, but his is a benevolent immaturity, while Gene's is decidely malevolent.
"As Ronald Weber writes in an article from Studies in Short Fiction, "It is Phineas's innocence that Gene cannot endure. As long as he can believe Phineas shares his enmity, he can find relief, but with this assurance gone, he stands condemned before himself and must strike out against his tormentor."