Depends on how "drinkable" you want it. Flammability = high alcohol. As you get above 100 proof you get more and more flames and more visible flames. A lot of bartenders use Bacardi 151 because it's high enough in alcohol to produce a visible flame but not so high that you can't drink it. Also, B151 layers nicely on flaming shots and cocktails and adds a little sweetness. If you go above 151 (77% alcohol) you start to get less and less drinkable liquors. Everclear has 70% and 95% versions, but you can't drink the 95% straight and it's not particularly safe to mix as a layer. Plus it's illegal in some places. I've only ever seen it as a base for big jugs of punch or lit by itself just to show it burn.