Replying to Need help w/ stiffness of boot

So I've never really bought boots before...I just moved to Big Sky and am an all-mountain skier. I like throwing 3's and 5's and skiing switch, I love charging and skiing the trees. I know a lot of this pertains more to which skis I buy, but I am kind of lost with what I should be looking for in a boot...

I've just used other peoples boots or hand-me-downs for a while. Should I be looking for something that flexes and lets me lean forward, or something more stiff? Is this totally up to personal preference, or are there benefits and drawbacks to each? Thank you!