@Supernoob I have gallons upon gallons in storage in medical grade freezers. I have it down to a science. I purchase like
@Jimi D, 100% PG. I always get 100mg, as it seems to be the sweet spot in strength and safety. 100%PG should be the choice unless you are PG sens. As Jimi stated, PG is MUCH easier to work with, and PG based NIC will store better, and quite a bit longer than VG based.
The biggest issue with 100%VG based NIC is when very cold (as your NIC should always be), it is VERY thick. This makes not only using it a chore, but also thoroughly mixing it up BEFORE using (to prevent "Hot Spots"), equally difficult. Because it is so thick, most people have to fully thaw it out JUST to be able to mix it, and use it, and repeated freeze/thaw cycles WILL rapidly speed the decay of the NIC.
Purchase your NIC of choice, and break it down into smaller glass bottles with good caps. I go a few steps beyond that, and use -55F medical freezers, top of each bottle with Argon gas, and cap and tape.
How much you purchase will obviously dictate how concerned you are about long term storage. A fridge could be fine for a small "working" bottle, but if you are storing, and/or long term storing, the freezer is really the only way to go.
Light, heat, atmosphere (air) are the three things which will oxidize your NIC. Minimize, or eliminate them as much as you can.