October Novel Prep Challenge

I'm writing my novel from two POVs -- the protagonist and the antagonist. I'm okay with that, I (think) I know what I'm doing. But I can't decide how to differentiate between the two narrators. They will be separated by new chapters, and the language and way they speak will be different, but I mean, how do I title each chapter? I don't know whether to use their name, or initial, or just a title, and let the reader figure it out. I'm not sure. What does everyone think about this?