Depends on what sort of liquids you want to make, but VG-nic tends to store better than PG-nic since it is thicker. Molecules just can't get around as easily to react with O2. Sets up like glue in the freezer. PG stays pretty liquid. I have several different nics from different sources, and VG-nic always remains unchanged. I have some that are 3.5 years old still as fresh as the day I got them. PG-nic really depends on the purity of the nic. Some PG-nics that were very pure also remained unchanged, some went orange from oxidation...but turned into a delightful tobacco liquid in flavor. I think much of what we like in the taste of tobacco is from nicotine oxides. But its not for everyone. Takes very little oxidation to strongly color a nic-base. I doubt the nic content changed more than a few percent.
If I make a 12 mg juice, 30 mL, I will only use 3.6 mL of nic base, so it hardly matters if the base is PG or VG...that is if I don't have a PG aversion...but I do so I only use VG nic. Plus the certainty that it will store virtually forever in the freezer.
@StormFinch: Thank you so much, you sexy-birdie-genie-thing!

Better vaping through chemistry! If I could get you to introduce me to my students, perhaps they would actually listen to me!