The standard is "use what you would drink."
I use 10 shots (15 ounces) of hot brewed Starbucks Espresso at the bottom of the secondary in a 5 gallon batch, for the AHS Redhook Double Black Stout clone. Double Black was a collaboration between the Seattle based Redhook and Starbucks. As SWMBO's favorite, this is the only brew that is firmly in my rotation.
Drinking: Innis & Gunn Rum Aged; NB Conundrum Session IPA; Bush de NoŽl (Scaldis NoŽl); Innis & Gunn Bourbon Stout; Theobroma; Redhook Double Black Stout IV; Leftover ESB; Cuvťe Des Trolls; St. Landelin la Divine Inspiration; Hibiscus Mango Blonde.
Secondary: Victory HopDevil.