Well if you ask me, I would like to say both but since I have to choose I would choose suppi. Suppi is supposed to be the serious and smart guardian. He is supposed to be thoughtful and has more of a mature nature, making him the direct opposite of ruby moon. He is, in a sense like the most level-headed person/guardian in the family. However, thanks to Eriol's very twisted mind, he has a thing with sugar. Once he eats sugar, he becomes sugar-high...literally. He suddenly uses a very cute voice and starts going around looking for sugar or anything that has sugar in it. After awhile, however he falls asleep.
About Kero, however, is roughly the opposite of suppi. He is mad about food and is very funny. However, if the occasion calls for it, he can be very serious. He is more of a happy-go-lucky guardian, while suppi is one who is serious and does not really like to listen to nonsense. So in the end, my vote would go to suppi