Replying to What boots??

Okay, when it comes to buying boots, i have no clue what im doing and i just go with whatever the slaes person is telling me, so i just need to know, what kind of boots would be better for me, sitff flex, mid flex what size and stuff like that

i weigh around 150 and im an agressive skier probably going to do 70% all mountain, i just need a little bit of info before i walk into the sotre and buy my boots.

any help at all would be great