Lots have mentioned that VG makes more vapor, and PG is debatably a better flavor carrier.
A couple other things to consider:
- Some people have an allergic reaction to one or the other - so if you find some allergic reaction to vaping, try heavy PG and heavy VG liquid, to figure out which one.
- VG is MUCH thicker, so it doesn't "wick" as easily in devices that need wick to suck liquid up into the coils. People who are vaping 100% VG liquid to make gigantic clouds are typically doing it in drippers - so they don't have to worry. But if you're using a tank system, you probably need a thinner liquid to flow right.
I mix my own, so if I feel like it, I can mix up some 42/58.