I've experimented a bit and landed on https://en.wikipedia.org/wiki/Everclear_(alcohol) https://en.wikipedia.org/wiki/Everclear_(alcohol) for most of my neutral

I've experimented a bit and landed on https://en.wikipedia.org/wiki/Everclear_(alcohol) https://en.wikipedia.org/wiki/Everclear_(alcohol) for most of my neutral spirit bitters. But I've also had success with lower proof vodkas. The more "earthy" bitters especially its hard to tell the difference. Some of the more herbal or lighter bitters you can sort of tell. There are also bitters recipes that use whiskeys that are quite good as well.