The only TFA flavor I use is Hibiscus and CAP's Hibiscus. However, both require 18-19% flavor, at least to my liking. Out of those two, I prefer the TFA. Most of the FA flavors require 3-5% only. Therefore, I prefer FA for high VG mixes. Besides FA's flavors are usually tasting like the real thing, which I can't say about other flavors I've used so far.I have not tried grape from any other source other than TFA.
Personally I like it and would recommend it if you want some delicious grape.
https://shop.perfumersapprentice.com/p-7546-grape-candy-flavor.aspx