I have made shortcake a few times using Bisquick, but I've found the shortcake came out tasting too dry and just a bit bland.
I think this FoodBuzz blogger, Susan Filson, has the right idea. In this post, she writes:
Some [recipes] call for an angel food, pound or sponge cake for the base. I prefer the traditional biscuit shortcake. It is firmer, thus, it doesn't fall apart when you put the berries inside. Also, it isn't as sweet as a regular cake, allowing the strawberries to be the star of the show. I like to adorn my shortcakes with nothing but pure and rich, freshly whipped cream. This is the kind of shortcake that I grew up on, and I'm sticking with it!