ANSWER: Both are correct, but Holy Spirit is preferable, because the word "ghost" has in modern times suffered a degradation. You would be shocked to hear John 4:24 quoted thus, "God is a ghost." Hence the American Revision invariably says Holy Spirit. The English were more conservative. Probably they thought it would spoil too many good hymns, such as Bishop Ken's Doxology, to let the term ghost go out of religious use.
— Steele's Answers, p. 227.