Ralph and Rekieta are two sides of the same coin. Both ultimately engage in the same sort of self-destructive, malignant behavior. Both have substance abuse issues, low-impulse control, extreme resentment towards women, lash out constantly, manipulate, lie, and hurt the others around them, both physically as well as mentally. But the underlying mechanisms for how each functions are worlds apart—which makes the comparison really interesting.
The core difference comes from the fact that Ralph knows he's a sack of shit and is ashamed of that fact. All his actions are meant to cover up his feelings of self-hatred. Ralph will try to improve and feels regret about his actions, but inevitably fails to meaningfully change his behavior because he lacks the proper mental discipline and control to accomplish it. Each failure feeds Ralph's self-hatred even more and he spirals further down.
By contrast, Nick unironically sees himself as superior to everyone else. Nick does not feel shame for his actions and legitimately seems to be incapable of honest self-criticism. Nick cannot change to improve himself because he feels there's nothing he needs to change. Nick really believes he not is at fault for his own condition and externalizes that cognitive dissonance by blaming other people (see: Aaron) or abusing substances. Unlike Ralph, whose actions are meant to cover up his own feelings of inadequacy and shame, Nick's actions are meant to affirm his own sense of superiority and lash out against those who threaten it.
Ralph ends up the more sane of the two, because at least Ralph wants to do better. Nick doesn't.
The Ralphacurse!