Super quick off my head...
PG: Propylene Glycol - thin, made from animals, and higher chance of allergic reactions, but supplies the liquid with a killer
Throat hit, and not a massive vapor.
VG: Vegetable Glycerin - thicker, made from well Veggies, sweeter, produces a lot of vapor, not extreme with
throat hit, but for me is better over PG.
Alot of liquid suppliers suggest using a 80%PG / 20% VG Blend, but for me I like 50/50 and more times 20% PG / 80% VG
To me VG is cleaner tasting, but it can also clog an atty faster when using 100% VG.
I've tried both 100% PG and 100% VG and find no difference in flavoring unless it comes to Coffee or Chocolate flavoring, then I would suggest more PG.
Any reason to why you ask?