Q: What key do you sing in in?
A: The original, I guess . . .
This answer is almost always wrong. The reason is because until you have tried the song in a few keys you can't say for sure. And most people just don't go to the trouble.
Take the advice of my friend and colleague Donna McElroy here . . .
http://donnamcelroy.net/2016/09/cover-tunes-and-your-best-key/