Nicotine Strength
The right strength depends mostly on your device. Low-power pods pair with high-strength salt nic; sub-ohm setups pair with low-strength freebase. Canada caps nicotine at 20 mg/mL.
Freebase
For refillable tanks and sub-ohm setups. The higher the strength, the harder the throat hit.
Salt Nic
For pod systems. Smoother than freebase at the same number, and absorbed faster.
Choosing a strength.
How strength, device and nicotine type fit together.
Nicotine delivery is strength multiplied by vapour volume. A sub-ohm coil vaporises several times more liquid per puff than a pod, so 3mg through a sub-ohm device can deliver as much as 20mg through a small pod. That is why a strength is never chosen in isolation — it is chosen for a device.
12mg exists in both families and they are not the same product: freebase 12mg is harsher and absorbs slowly, salt 12mg is smooth and fast. Check which one you are buying — the number alone will not tell you.