For early HR, Wroggi is pretty great, negate poison is fantastic and razor sharp is crucial on DS since they lose sharpness pretty quickly in demon dance. Later on, there are so many great sets it almost doesn't matter until G-rank; personally I got A.Los and later gemmed in Bombardier with the help of a talisman. Although; if you don't mind the lack of HGE or gemming out... whatever it is that it inherently has, you could gem it straight into the set's slots.
Bombardier is a key skill in using slime weapons btw; I forget whether it increases how quickly the slime is applied (increases the slime value on the weapon) or if it increases the explosion damage by 30%. There's a lot of confusion around it.