Which is correct: "If it were I" or "If it were me"?

Solution 1:

It's "if it were me", as opposed to "if I were it". Compare: "If I were him" sounds good, but "If I were he" does not. The first pronoun is in the nominative case, the last one in the accusative. Also, see this.

Solution 2:

As you stated in the question, “if it were me” is more common. I would use this form.

However, which is correct seems to be a common topic of debate. See Wikipedia for an analogous question about whether “it is I” or “it is me” is correct. Using “me” is more common, but some grammarians consider using “I” is the correct form. I am pretty sure that those grammarians consider that “if it were I” is the correct form.

Solution 3:

As others have said, no doubt the technically correct expression is "if it were I" because the verb is copulative. Some might argue that "me" is more common, and "I" is rather pedantic. However, if we go that direction one might also question the use of the subjunctive at all which is also verging on archaic.

If you are going with wrong, but popular, I'd recommend "If it was me..."