Friend problems please help?

ok at my school people are really backstabbing and i am having a hard time trying to work out who my friends are. One of my friends (friend A) used to get angry at the smallest thing and wouldn't talk to me for days, now she has realised what she is doing and has tried really hard to stop, but she often says things i don't like and we have very different views on things, i know that preciously she has talked behind my back and i'm not sure if she still does, Friend B always talks about friend A behind her back but claims she's nothing like her, she can be nice but she acts really childish and can be really irratating and says things that i think are unreasonable. Friend C is really nice and never talks about people behind their backs but she can act really childish and immature, friend D is really quiet and we barely talk but she is really kind, friend E is really nice and we get on really well but she often talks about people behind their backs and has what i think are unfair veiws on people, Friend F is really nice and never back stabsm is she my only real friend? who should i try and build our friendship and who should i try to avoid? please help?