Which is okay in conversation, but in writing, your pedantic editor or proofreader would probably inform you that it is considered poor style to end the sentence on a preposition. So he's basically trading one error for another.
Who/whom is indeed awkward at first to remember, but the phrase "for whom" tends to sound better on the tongue than some of the others due to its inclusion in the title "For Whom the Bell Tolls," a popular novel (or "popular Metallica song", depending on your age).
Who/whom is indeed awkward at first to remember, but the phrase "for whom" tends to sound better on the tongue than some of the others due to its inclusion in the title "For Whom the Bell Tolls," a popular novel (or "popular Metallica song", depending on your age).