Everyone has different preferences for how much PG or VG they use in a mix. Some are also more sensitive to one over the other, for example, I use a higher PG ratio in my final mix because I'm more sensitive to VG. In amounts over 25%, I cough a lot and feel like I have a really bad chest cold. Others are the opposite. Those with PG sensitivities can experience tinnitis (or flare ups of), coughing, tight chest. Still, others prefer to chase clouds, so they use a max VG final mix.
I buy nic in PG base. It's thinner than VG, which makes it easier to pour, and, as mentioned, I use a higher PG ratio. Those wanting max VG will usually purchase nic in a VG base.
Regardless of what someone else uses as their base, you would basically/typically mix the flavoring with the same % someone else uses in a recipe.