Depends, really. If you don't have plants, it doesn't really matter if you use one or the other (or one of each). If you have live plants, you don't want to use the goldfish cartridge because it will absorb nutrients that the plants need. But the tropical fish one contains carbon and it's typically not reccomended to use that in a planted tank for the same reason; you actually shouldn't need carbon at all unless you're removing medication from the water.
What I've done with mine is cut into the little pockets to remove the carbon, replace that with a bit of filter floss, and sew it shut with monofilament line. After this media wears out, I may actually skip the cartridges and just cut some aquarium sponge to fit because retrofitting the cartridges gets a tad bit messy.
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