What is the difference between a Showdown and a Challenge?

Challenges and showdowns are two types of competitive quiz playing on Sporcle. In a challenge, the two people in the challenge play the same quiz, on their own time, and whoever has the better score after both people have completed the quiz wins. In a showdown, the two people in the showdown play the same quiz, at the same time, and whoever gets more correct answers before the timer runs out wins. Both count as a quiz play for badges and overall quiz stats.