Which of these is correct: "neither of you are" or "neither of you is"? "Which (one) of you are" or "which (one) of you is"? I think it should be "is" in both cases, since "neither of you" is not a second-person reference, and therefore should not take a second-person verb.
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'is' denotes singular, 'are' plural
So "Which one of you is .." is the correct from.
But, "Neither of you are .." is ONLY the more correct form. I could say "Neither of you are my first choice." or "Neither of you is the one I would choose."; both being correct form.
As for the correct verb form after which in a question, it depends. If you want to refer to a singular person, you should ask "Which of you is...?" But if you want to refer to more than one person, then the plural form is acceptable, as in "Which of you are ready to follow me?" Note, however, that this form sounds a bit stilted; a more natural way to ask this question would be "Who is ready to follow me?"