I Have A Rather Bad Looking Boil On The Underside

I have a rather bad looking boil on the underside of my large stomach.has opened and is black in middle green around the black and dark red about an inch around that and then pink 3-4 inches completely around it. Have had them several times in different areas. I have a full prescription of both clindamycin 150 mg 3x day for 14 days or metronidazol 500 mg 3x day for 10 day. Question is which should I take