"Which" is fine, but that word has to modify a noun, rather than being used alone:
"Which team won the game, the Mets or the Mariners?"
If you don't want to specify a particular class of object, you can use something like "which one" or "which of them" instead:
"Which of them won the game, the Mets or the Mariners?"
"Who" works, too, and sentence B is perfect. I'd say it's more likely to be used just because it's shorter.