If you care about performance, you would use neither format.
Developers choose json over xml because using it and dealing with it is more lightweight than dealing with the very baroque xml. The fact that the typical json payload is 1/2 the size of xml is just a bonus.
Developers choose json over xml because using it and dealing with it is more lightweight than dealing with the very baroque xml. The fact that the typical json payload is 1/2 the size of xml is just a bonus.