We can use which and what before nouns to ask questions about people or things.
- Which teacher do you like best?
Which colour do you want — green, red, yellow or brown?
What writers do you like?
What colour are your girl-friend’s eyes?
We usually prefer which when we are choosing between a small number, and what when we are choosing between a large number. Before another determiner (for example the, my, these) or a pronoun, we use which of.
- Which of your teachers do you like best?
Which of them do you want?
We can use which, what and who as pronouns, without nouns. We use who, not which, for people.
- Who won — Smith or Fitzgibbon?
Which would you prefer — wine or beer?
What would you like to eat?
We usually use who, not whom, as an object.
Who do you like best — your father or your mother?
(Whom do you like best . . . ? is very formal.)