First, how is this unbiased? Well, I have not played either game, so, my observation is completely unbiased.
Win/Tie
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Graphics: Sony. Based on screenshots alone.
Price/Value: Nintendo. You can't beat a $0.99 unless Sony decide to give it free like so many other titles.
Gameplay: Tie. I have played neither.
Replayability: Sony. Track builder alone will make you spend more time building tracks than actually karting.
Sound: Tie. Both sound about the same with sound off.
Verdict: Sony won. Sony edges out slightly against Nintendo even thought it cost at least 20x more at discount prices. You are buying quality here.
Here are 2 screenshots to prove that Sony makes superior karting game.























