pg is on the thinner side, less vapor, more throat hit but lots of flavor
vg is on the thicker side, more vapor, less throat hit a little less flavor.
A ratio recommended by some
juice suppliers is 70pg/30vg or 80pg/20vg. That's not too thick, not too thin so it doesn't clog cartomizers. But it really is very subjective. That's why it's good to order small sample size bottles in varying nicotine strengths and ratios.