“Which for That. “The boat which I engaged had a hole in it.” But a parenthetical clause may rightly be introduced by which; as, The boat, which had a hole in it, I nevertheless engaged. Which and that are seldom interchangeable; when they are, use that. It sounds better.”
Excerpted from: Bierce, Ambrose. Write it Right: A Little Blacklist of Literary Faults. Mineola, NY: Dover, 2010.