I know you've discussed POV before, but how do I know whether I should use first-person or third-person in my novel?
First-person limits your writing in many ways. Because the story is being told by the main character (usually), you can only disclose what they experience. So if you need a scene that does not involve your main character, you have to have someone tell them what happened. Also, your secondary and supporting characters are a little harder to develop because you don't get inside their heads. We learn about them as they interact with your narrator. Some readers really hate first-person. (The woman who gives me pedicures refuses to read anything in first-person.)
The advantages of first-person is it often brings the reader in closer to the main character, letting them identify with them more. First-person goes in and out of style, but it is currently the favored POV for middle grade and YA novels. A very popular example of first person is the Twilight series by Stephanie Meyer.
Third-person omniscient allows you to share the experience of a variety of characters. You can look at events from various viewpoints and listen in on the inner thoughts of almost anyone in the book—including the antagonist. This often makes it easier to show motivation and add dimension to all your characters. The difficulty with third person, however, is that it can distance the reader from the main character. It also lends itself to "telling" rather than showing. A popular example of third person done well is the Harry Potter series by J.K. Rowling.
How do you know which is right for your book? Depends on the mood you're trying to create. Read several popular books in your genre that use different POVs and analyze how it makes you, as the reader, feel. Then use the POV that does best what you want to accompolish in your book.
Another option is to write the first chapter in both first and third POVs. Which one do you like best? Share the chapters with a few friends or in your critique group. Which did they like best and why? That should give you the answer to your question.