Should I buy pigment-based inks or dye-based inks?
Dye inks are absorbed by the substrate (paper, vinyl, polypropylene... etc), they give very vibrant colors, but colors are fading easier and tend to bleed in when in contact with water. You can use dye-based inks when your labels will be used indoors only and when they don't get in contact with water or other liquids.
Pigment inks are layered on top of the substrate, they have a better resistance to UV light and abrasions and they can better withstand water and other liquids.
So to wrap up! Use dye inks for short term indoor labels that don't get in contact with liquids and pigment inks for outdoor labels or labels in with a longer life expectance.