Depends on how much time you are willing to put into it I suppose. My son does well with an animal he can bond and interact with ( just got him a guinea pig and they have already bonded well) gerbils aren't very keen on being handled a bunch in my experience. I think they both eliminate about the same quantity, but with a guinea pig it can be trained to use a potty box with some effort so less cleaning time. You can find used large cages designed for a guinea pig for cheap on fb market place (i did 😁) food cost and bedding will be about the same for both.
Guinea pigs are friendlier and you can hold them. Gerbils are more skittish. Exotics and aquatics have different deals for cages and pets. Sometimes you can get the pet free.
Guinea pigs poop a lot. Like A LOT. Its like constant. You'll need a bigger cage for guinea pigs too. Gerbils are cheaper, eat less, poop less. Can use a smaller cage.
Guinea pigs are more interactive and live longer.
Guinea pigs are better pets. My daughter bought a guinea pig there with cage, and food + supplies for around $80.
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