Complete a chart listing the advantages and limitations of each voice. For instance, in third person omniscient you can describe more of what is going on outside of the main character's sight than if you were writing in first-person. If a first-person narrator is telling a your story, you are limited to what she sees, hears, thinks and feels. For instance, the narrator would not be able to describe what life was like for the protagonist's family during the Civil War era if she was not born during that time. Review the chart to see which voice has the most advantages.
Write a few pages of one chapter in several different voices. Compare and contrast the samples, reviewing for cohesion and readability, how sympathetic the narrator's voice is and what details are included or excluded.
Ask readers in your target audience to give their feedback. Send your novel to a few authors who write in your genre or people who often read this genre. Tell them which narrative voices you are considering, and ask them to tell you which voice would be most appropriate for the novel and why. Give them the samples you drafted in Step 2. Ask them to choose the most effective sample and explain why it is so effective.