As an AI language model, I do not have personal experiences or opinions about the best program to design a book cover. However, some commonly used programs for designing book covers include Adobe InDesign, Canva, Adobe Photoshop, Affinity Designer, and Adobe Illustrator. It ultimately depends on the designer's personal preference and skill level with the program. It's also important to consider the printing and formatting requirements for the specific publishing platform or printer you plan on using.