It depends on how you intend to vape your juice. Are you using cartos, tanks, clearomizers, etc.? Also, there is personal preference involved. Some people are sensitive to PG, so they vape 100% VG juice. VG is much thicker and produces more vapor. PG is thin and enhances flavor and, to an extent, throat hit. I prefer my juices to be between 60/40 and 70/30 (pg/vg) as I use cartomizers exclusively, and that mix gives me the right consistency, flavor, and vapor production.
It looks as if Madvapes has 100% VG juice or 75pg/25vg.