
You wouldn't know it as a casual player, but there are different stastics for each character when paired with a kart combo in Mario Kart World, so if you want to get the best stats when trying to play online and raise your point tally, its important to know are the details you need to make the best decisions possible.
The stats are only per character as well, so using a character in a different outfit won't change the base stats, so you can take the character you either like best or want the stats of, and wear any of its costumes with no issues whatsoever.