>>132916570True that, but their failures have their reasons, seeing as Kyubey only contracts to people have have problems and can be tempted to be a Magical Girl and a Witch.
Madoka is an overly-sacrifical martyr who will disregard herself for others. Seen very many times in the series, Homura says it herself once.
Sayaka is a very idealistic girl, seen many times as well in the series. Ex. She contemplates about the idea of wishes being given to people like them in episode 2, not being able to take having no soul, etc. Many of her ideals are broken during the extent of the series.
Mami is the senpai figure yet doesn't have anyone to be a figure to, she's lonely. She thinks of herself as reliable and is the leader of the MGs. She, however, is very emotionally scarred. She also lost her parents in a car crash and has been living alone fighting witches since, and was abandoned by Kyoko (The Different Story Manga/ Drama CD)
Kyouko is another idealistic girl, and is very similar to Sayaka in many ways. They both have their sense of justice, yet Kyouko was already scarred before the series, due to the death of her family, hence most of her ideals were broken.
I don't even need to explain Homura.