PG and VG are similar chemicals in some ways, PG = propylene glycol, VG = propane 1,2,3 triol. Both sound fairly grim but so does anything when called by its chemical name, eg dihydrogen monoxide or hydronic acid (water).
Both are solvents, diluents, have a high carbohydrate content, vapor carrier agents, vaporize well in air, and are virtually inert in humans. In other words they are ideal for this job, since they dissolve some things about as well as alcohol, keep them in solution well, create a nice-looking mist when heated, and are more or less inactive to humans (meaning they are approved as safe to inhale or ingest in any way as most people are tolerant to them).
As far as preference goes, it's purely a matter of taste, like anything else. A 50-50 mix is popular, as is 90-10 PG-VG. 100% VG is fine, however it seems a good idea for that purpose to add something like EM, ethyl maltol, or PGA.
VG may be more acceptable for those who seem intolerant to PG. Or, people might want to use a vegetable product instead of a manufactured one. In that case you should probably
buy something
named specifically as Vegetable Glycerine on the label, since it can be manufactured synthetically like anything else. All 'VG' is not of vegetable origin despite the name.
For practical purposes it works as well as PG. It's slightly thicker so benefits from dilution. Mixed with PG it gives better TH. It's a 'cooler' and 'sweeter'
vape although many would not notice that, it is a matter of tiny percentages. Some people are VG-only vapers, there is a social group for that. You can get 100% VG liquids. Flavors are currently very restricted though, so it is sometimes necessary to add PG-based flavors, if you don't mind doing that instead of hunting for flavorings with no PG.
