JPG
PNG
GIF
I used Photoshop to create a transparent background for this cookie. Comparing all exports, it is clear that the PNG has the highest quality. Though I cannot really account for the JPG, the PNG is smoother along the edges than the GIF. The GIF photo seems to have added some additional white pixels not included in the original file. There is a faint, but noticeable white border around the cookie in the GIF that is not present in the PNG version.