This is really subjective. Some prefer a higher pg, some prefer a higher vg, some prefer a balanced 50/50 ratio. This is based on individual's past experience.
Pg generally is considered a better flavor carrier than Vg. Some folks are sensitive or even allergic to it. It contributes slightly to the throat hit.
Vg is the vapor maker. It is much thicker than Pg, so many tanks have difficulty wicking the thicker
e-liquid. Works well for those who use drippers.
I would guess that the majority of e-liquids are close to a 50/50 Pg/Vg ratio. A lot of online e-liquid manufacturers (ie Dripeez, Virgin Vapers, VapeRite) allow you to choose the Pg/Vg ratio when you custom order.
I prefer a higher Vg ratio, myself. Too high Pg and I detect too much harshness for my tastes. I also like those companies who use all-organic, all-natural flavorings rather than artificial flavorings.