Do you recommend butter? Or a vegetable shortening? Or both?

If you want the same texture of cookie that the author intended, you will stick with the shortening called for in the recipe. There are subtle differences between butter, margarine and shortening which do make a difference in the final product. Shortening is 100% fat, butter and real margarine must be a minimum of 80% by law. However, many of what you think of as margarine is actually legally a spread, and will contain less. The balance left with butter is made of milk residues, water, and possibly salt. Margarine will be mostly water, and of course whatever vegetable fat was used, plus salt. Products made with shortening tend to be softer in texture than those made with butter or margarine. Shortening also melts at a higher temp than butter or margarine, so that affects how much your cookies will spread in baking and how thin or thick they end up being. This cookie is highly flavored with coffee and chocolate, so the butter taste would be lost entirely. So it's not really worth it to substitute in this recipe. Just use solid vegetable shortening. If you really must substitute, it makes better economic sense to go with a high quality margarine as well. Since you won't taste it, there's no point spending the money for butter.

I would assume that by "shortening" the author means Crisco, the actual meaning of the word is all but lost these days.