Is it better to use coffee extract or instant coffee for a buttercream recipe?

or you can dilute the coffee in a very small amount of hot water before adding.

I use a quarter teaspoon of Via coffee (from Starbucks) or instant espresso in the powdered or granulated sugar ...whichever you use.

Is it a swiss meringue buttercream? If you use instant coffee you have to add when its warm in order for the coffee to melt. If its a simple butter and confectioners sugar recipe you should probably use coffee extract, otherwise you would end up with coffee granules in the frosting.