Answer: For my opinion I would pick Amaryllis.
The reason why is because Amaryllis sounds more happier. I am a very generous and joyful person so that's would I would go with. But if I felt down and sad and didn't want to be around anybody I would pick Nightshade. The reason I would pick that is because when I feel down and shows a resemble of darkness just like the nighttime. Hope this helps!
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I am joyous to assist you anytime! (: