Should I do massacre on Jevil? Or pacifist?

Should I fight him? (Massacre) Or should I spare/pacify him again? (Pacifist) Which should I do? I get devilsknife if I fight him and beat him. I get Jevilstail if I beat Jevil without needing to fight him and sparing/pacifying him. I dunno what to do anymore... I'll be waiting for a few responses... I will attempt to beat him again on my main...