vg is thinner and gives more flavor and throat hit, vg is thicker and gives more vapor but not much throat hit or flavor. You can get liquids 50/50 (which is what I typically do) or some sites allow you to customize the mix. So some people prefer 70%pg and 30% vg, or visa versa. That part is personal preference. But if you use a tank with a cartomizer and your liquid has a lot of vg and is thicker, you may need two holes or one larger hole in your cartomizer and they seem to clog up the cartomizer faster. If you have a tank like the vivi nova, liquids with a lot of vg may not wick as well. It's all a matter of personal taste, really.