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: Cherry Porter; AHS SuperCaliFugglisticESBAledocious; Rafikah Rose's GF Pear Ale; NB La Petite Orange Blanche; NB The Plinian Legacy; Val-Dieu Triple; Redhook 8-4-1 Expedition Ale; Avery The Czar Imperial Stout; MŁnchen Haken Besonderes Bitter (Redhook ESB II). Bottled: Bush de NoŽl (Scaldis NoŽl) (first taste 16 November 2015)