Santa doesn’t have a favorite elf, he loves all of his elves.
But because no two elves are identical and each elf has their own unique personality, Santa loves each elf differently. As far as having a favorite elf, love and favoritism do not mean the same thing. Santa doesn’t set out to have a favorite elf, but sometimes it just happens. For example, after a long night of delivering gifts, Santa might favorite the elf that brings him a nice cup of hot chocolate. But his favorite elf changes all the time and can change by the hour, the day, the week, the month, or the year.
Learn more about the Christmas elf on Wikipedia.