Besides the obvious reason of decapitation, why a machete? My preference would be a crowbar. It has multiple common uses such as prying, chipping, breaking into places, anchoring a climbing rope, as well a being a sturdy bludgeoning weapon. Granted, a crowbar in one hand and a machete in the other would look awesome (though perhaps not to efficient).
A crowbar is blunt, and thus will cause more splattering of infected tissue.