Impossible. I never met a cookie I didn't like. Some of my favorites:

The macarons from Gérard Mulot in Paris. My mother's date filled oatmeal cookies. Chocolate chip cookies, still warm from the oven. Walker Shortbreads. Macadamia nut shortbreads from Honolulu Cookie Company. I don't know if they still make them (I used to buy them at Jewel in Chicago and I don't shop there anymore): President's Choice Chocolate chip cookies. The lemon ricotta cookies at Nordstrom Cafe. My own chocolate peanut butter swirl cookies. Raspberry nut delights (layers of shortbread, raspberry jam, coconut and pecans). Food for the Gods (an incredibly buttery date bar found in an old Filipino cook book).