PG gives greater throat hit, less vapor, generally passes flavors better (in VG you have to crank up the flavor %).
VG produces more vapor, less TH. Some people note a slight oily sensation from
vaping VG.
Some people have sensitivities to either PG or VG, need to minimize the intake of one or the other. Otherwise, mutts like me can use either fine.
For people with no sensitivity, a mix of about 70% PG/30% VG to 80% PG/20% VG is often pretty popular, hits the "sweet spot" combination on TH and vapor.
Over time I've found that TH doesn't matter much any longer,
vaping 0 - 60% PG depending on what I feel like mixing.