PG vapor is what hospitals use to deliver inhaled medications, even to lung transplant patients.
PG is thin, lets through the most flavor, most nicotine TH, most nicotine irritation and makes thinner looking vapor
VG is thick, dulls everything PG lets through and makes thicker looking vapor
Most people use blends. In slim ecig stuffing cartomizers I use 20% or less VG for a thin
juice that keeps the stuffing airflow good for a week. On an atomizer I use up to 50% VG because a couple of juices I like only come as 50/50.
tanks and reservoir cartos are happy with 20-30% VG, may leak more with 100% PG, may be able to use some 50/50 juices. Some vendors thin their high VG juices so it depends on that too.
When I bought my first ecig, I bought mainly PG with a small bottle higher nic and a small bottle lower nic and VG. That way if I needed less nicotine or less hit I could use the lower
juice or mix it with the others. My tongue got a bit sore from nicotine in the 100% PG but the hit was right. Since I was using an atomizer I tried 70PG/30VG juices and liked them a lot. In cartomizers (which I mostly use now) I found 20% or less VG worked better for me.