i feel both will be alost equal........but a.m.u assinged on the basis of BE will be slightly larger than tht of c12 as the binding energy(per nucleon) of c is greater than that of be...........hence more will be the mass converted ta energy ..........hence lessr the mass per nucleon......therefore lessr the amu(on basis of c12)...............hence amu on basis of BE will be more than tht of c12