The most common site of fracture neck of the femur that causes avascular necrosis is -: (A) Sub-capital, (B) Intertrochanteric, (C) Trans-cervical, (D) Basal
Answer is A. "The more proximal the location of a femoral neck fracture, the more likely there is to be nonunion and/or AVN". — Musculoskeletal trauma

Thus non-union and AVN will be most common in subcapital fracture and least in basicervical fracture.