Hazel is DEFINITELY the name to choose. I can "see" Hazel as a deep thinker who doesn't fit in well and who doesn't have friends.
Regan is a popular, cute, perky name.
HOWEVER, if you wanted to build an awesome contrast, pick Regan, make her cute and perky but with this intelligence she hides. Maybe her Dad's a hot model and her Mom is some kind of super intelligent scientist.
regan is my favorite name, so i'd go with that one anyway. as a writer, i try to pick modern/cute names for my characters. however, hazel IS more laid back and old fashioned if you want the character to be truly someone who doesn't fit in well. i'm still optin for regan though. it's cuter. hehe.btw, hon...i LOVE your questions. seriously. i hope i get best answer for some of them as i am a fellow writer too. :)