I am usually a PG vaper, all the way, but I gave a VG mix a try for a tasty new flavor being sold at the vape shop. Holy cow, I was satisfied with the flavor but not the change in make-up of the liquid. I use a wide coil tank that heats my liquid pretty well. It makes the taste simply amazing. But when I used the predominately VG based liquid it seriously scorched my coil. I can use one coil for about 3-4 weeks with the 100% PG liquid I usually vape, but I was cleaning or replacing my coil 1-2 times a week with the VG mix! What?! I was so frustrated. I felt like I was screwing something up with my battery, it just freaked me out, I thought I was going to short out my unit. So here is a bit of a (slightly biased) run down on the differences and you can find what you might be looking for.
Propylene Glycol or PG eLiquid is a flavorless, odorless substance that gets flavored and mixed with nicotine for vaping. PG is a thinner liquid to heat in your vape tank and provides a nice throat hit and gentler, even keeled, taste. Many people find the PG eLiquid to be super satisfying if they are trying to drop cigarettes since the throat hit is more direct. I have found this to have a cleaner burn and it gets more evenly dispersed in the cotton coils.
Vegetable Glycerin or VG eLiquid is a really safely ingested liquid product which gets flavored and mixed with nicotine as well for vaping use. VG has a thicker consistency than PG and has a more rich mouth taste when vaping. For this reason it seems to me like it might not have as smooth of a journey through the cotton coils. Just because of the consistency the liquid may not move as quick when being heated.
This is just one opinion - but a lot of people prefer a VG mix for the sole reason of the mouth taste.
The way the clouds are produced with this thicker liquid provides more taste sensation to the palate. So it really depends on your reason for vaping as to your preference in how your puff tastes and satisfies. If you are looking for the vapor to give you a direct throat hit so it is almost a sharper cigarette feeling, then a 100% or predominately PG eLiquid will satisfy your hankering. PG based eLiquids also tend to carry the added flavor in a purer manor, since the thickness cannot influence it. If you are vaping to get flavor above all, then a VG based (which is more popular in the industry) will get you the thicker flavor you're looking for. I for one do not know the science behind it all, I mean I'm sure it gets pretty technical. Not just in terms of an eCig, but the process in creating water vapor, come on, I don't have a masters in science. Okay but it makes sense though, think about it: if you heat pure water, it steams and evaporates and it's pretty much gone, yet if you're using an oil diffuser it kind of fills the air and lingers in the area. I don't know if my thought process is coming across well, but the sentiment and effort are there! If you think about it this way, the PG eLiquids just delivers the substance to the user, you taste it, and it is gone. Yet, if you use a VG eLiquid the substance sticks around and the taste provided is more palpable.
Another factor that comes up occasionally is the FDA and ingestion questions pertaining to each ingredient.
While Vegetable Glycerin is consistently added to foods and is FDA approved for consumption and Propylene Glycol is also an additive in many oral products, neither are technically approved for inhalation. A lot of users are more comfortable with VG as it does stem from natural products. PG on the other hand has chemical makeup and many speculate it is antifreeze, which is just simply untrue. Propylene Glycol, while not FDA approved for inhalation, is an ingredient in some prescription inhalers, which means to some extent is has levels of FDA approval, it just may be the level at which they are inhaled. Not sure if these factors are things that influence your choice in what to vape, but it is something to think about.
All that being said, the thick rich clouds and hit are what can draw users to a VG eLiquid, but I enjoy the thinner straight forward hit of a PG eLiquid. So the verdict stands, I'm gonna stick with PG, you decide for yourself what is more appealing.