Reasons to keep each? Well, honestly speaking here, I have never kept platies. the reason being, I don't like how they look. I have kept guppies. The reason I kept them is because I had a small tank and really thought they looked colorful and cool. The best reason to keep any fish is because you like it and want to keep it. Once you find a desireable fish, do the research, see what it needs to live hapily, determine if you merely want to keep it or breed it, then decide if you can afford to give it what it needs. If so, congratulations, you found a fish for the best reason; you will love it.