Make a single large batch of PG/VG mix. Split it into 5 portions. Add one type of nic to four of them and keep the 5th nic-free. That way each nic can be compared to the other as well as to a nic-free "juice".
I mixed up some 0 nic vg/pg 50/50 and have been vaping that on and off. I've also sampled just PG by itself and just VG by itself. (Straight VG still makes my nose run.) I also ordered up a fresh bottle of PG, as I was running low. I was surprised to find that the fresh PG tastes much better than the 2 year old stuff. Both are from Essential Depot. I don't know if the old PG went bad or picked up some taste through or from the plastic bottle.
I agree that the no-nic sampling is very useful in establishing a baseline for testing.