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: Val-Dieu Triple; Redhook 8-4-1 Expedition Ale; Avery The Czar Imperial Stout; MŁnchen Haken Besonderes Bitter (Redhook ESB II); Terrapin Reunion '10; Innis & Gunn Rum Aged; NB Conundrum Session IPA; Bush de NoŽl (Scaldis NoŽl).
Bottled: Innis & Gunn Bourbon Stout (first taste 28 November 2015).