I really like a lot of the badge designs, to be honest. It's hard for me to choose only one badge, so I'll just choose a badge set from one of the regions. If I do that, then it's really between both the Kanto and Sinnoh region. The Kanto region had some of the most beautiful, creative designs I'd ever seen. The Sinnoh region, however, had more pristine/clean badges. Not only that, but I thought the gimmick where the player could clean their badges was very unique and entertaining. I also liked the additional gimmick that the badges created music when you tapped them (1st gym badge has the lowest tone, 8th gym badge has the highest tone). All in all, I'd have to go with the Sinnoh region's badges simply because they were extraordinary.