Minako is the definite leader of the senshi, taking over when Usagi can't. She was the first senshi. Artemis found her in England, when she was originally modeling as "Sailor V". The usual trouble started, and she became the national hero, in a sense.
She, like most of the other senshi, has a troubled past life. We don't know what happened to her father, but she lives alone with her mother. Her mother is one of her biggest problems. Also, while still in England, she fell in love with one of her best friends. When she discovered he loved her closest female friend, she stepped aside, feigning her death in the explosion, to allow them to be together. Also, she has extremely low self-confidence. She seems to need to be around the others, and know that someone actually cares about her.
Personally, I dislike Minako in a lot of ways. Her constant boychasing (in the anime, she's somewhat better in the manga) gets annoying, I don't like the way she shows off, and she has a habit of misquoting nearly everything she says. She can be extremely silly, and as gluttonous as Usagi. Also, she isn't exactly a good student. Her absent-mindedness gets her into a lot of trouble, too.
However, my biases don't run too deeply. She has a lot of good points. Her leadership, compassion, and optimism springs to mind, as well as her ability to deal with everything thrown her way. She encourages the other senshi non-stop, even during the worst of their battles. She is extremely strong in the way she can pull the whole team around, as well as being physically able to take care of herself. She survived a factory explosion in London. And you have to wonder where she gets all of that energy!
I sometimes wonder just how deeply her abilities run. She seems to be able to feel things ("I'm getting a bad vibe from this place!"), and she always seems to know when Usagi is in trouble.