I've never done coffee extractions, but I'm pretty familiar with the flavorings available, because I love coffee vapes.
For a standalone flavor of plain, unadorned, black coffee, FA Espresso is the only one that does not taste like skunk excretions to me, the only one I can vape and enjoy all by itself.
For a standalone coffee flavor that's something more than plain, FA Tiramisu tops my list. Real tiramisu isn't a liquid, but the flavoring by itself gives me espresso, dark cocoa, a little cream, low-level sweetness, and a whiff of vanilla cake. Simple to mix, very tasty. Still, I prefer sweeter and creamier, so....
For more complex recipes, I have successfully used a bunch of coffees, but those two FA flavors make all my fancy coffees taste their best. I take the approach of getting all the additions right first, whatever combo I'm after: caramel, Irish cream, fresh cream, vanilla, nuts, butterscotch, cocoa, whatever... Starbucks has great ideas on their website. Once that tastes right, I add 0.25-0.5% of my coffee flavoring, whether it's FA Espresso, Tiramisu, or the TFA coffees I used to use. I'll always try a tiny amount before adding more. Sweet, creamy, dessert-like coffee vapes are my favorite, so I rarely go over 1% on the coffee part.