Based on your situation, both "want" and "need" can apply, but they convey slightly different meanings.
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Want: You desire a new basketball because the old one is worn out, implying it's more of a preference or desire.
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Need: You require a new basketball because the old one is no longer functional for playing.
If you're looking for a more urgent or practical reason, "need" would be more appropriate. If it's more about personal enjoyment or improvement, "want" fits better.
How would you like to express your feeling about the new basketball?