Cats and Dogs are quite clean since they clean themselves. guinea pigs are also clean. they clean themselves sometimes like cats and dogs and you only need to bathe them about once a month. and yes the cage can be messy but what do you expect? You can't train them to go outside like a cat or dog. Lol. plus some people train their guinea pigs to 'go' in a specific area of the cage which makes it easy to clean. Hope I helped :)
Fish. You don't have to touch them, or their feces. Cats and dogs are pretty easy to keep clean, as long as you clean up after them, but guinea pigs are disgusting. Trust me, you don't want to clean that cage every week.