Michael Vs. Sonny
At a first glance Michael and Sonny appear to be quite different. Upon further observation, however, they have some similarities. Although they are different in areas of personality, values, and their tempers, they are similar in areas of loyalty, their respect for their father, and their strong family ties.
Their personalities are quite different. Sonny is brash and arrogant, where Michael is calm and cool. When Don Corleone was in the hospital and Sonny is in charge, the family got kind of careless. He doesn't seem to care what could happen due to his actions. He wants to kill the police captain and doesn't think about the repercussions. Tom has to tell him that it wouldn't be good to kill a cop, but they end up doing it anyway. I think Michael was pushed into it because of his loyalty to the family. He is more calculating in manner.
Near the end when he "takes care of all the family business" on the day of the Baptism is a prime example of this. Because he was this way, the objects of his violence had no idea that it was coming.
Their values are another way that they differ. Michael is a man of honor. He doesn't run around having affairs with different women. He only marries twice because his first wife was killed in the explosion. Sonny is an adulterer. He is with another women during his sisters wedding, along with a few other times throughout the movie.
Their tempers were not nearly the same. Sonny had a bad temper, while Michael did not. Sonny's temper ended up getting him killed. He flew off the handle when he found out that his sister had been beaten and ran out of the house without anyone with him.