Patients randomized to RIC will receive one of two regimen types: the combination of fludarabine (120-180 mg/m^2) and busulfan (less than or equal to 8 mg/kg or IV equivalent) (Flu/Bu) or fludarabine (120-180 mg/m^2) and melphalan (less than 150 mg/m^2) (Flu/Mel). Patient randomized to MAC will receive one of three regimens: busulfan (16 mg/kg oral or 12.8 mg/kg IV equivalent) and cyclophosphamide (120 mg/kg) (Bu/Cy); or, busulfan (16 mg/kg PO or 12.8 mg/kg IV) and fludarabine (120-180 mg/m^2) (Bu/Flu); or, cyclophosphamide (120 mg/kg) and total body irradiation (greater than 1200-1420cGy) (CyTBI). A total of 356 patients (178 to each arm) will be accrued on this study over a period of four years. Patients will be followed for up to 18 months from transplantation.