grammar - A colon or a comma in alternative questions

Which punctuation mark should be used before the second part of the alternative question? Should it be a colon or a comma?

Eg:
What do you like best: pears or apples? or
What do you like best, pears or apples?

Which of these two question has the correct punctuation?

All gramma manuals I looked through say nothing about using a colon in alternative questions.

Thanks in advance, Vic.