It really depends on the torture method(s) used, but I'd probably go with killing an African child. It's not the ethnicity nor the age that matters, if you torture someone for a full day, you'll just cause permanent and severe mental and physical damage to them. Which is worse that taking a life, in my opinion, cause they'll be suffering for the rest of their life.
Plus, you'll be hearing their screams, begging to be released or killed, while torturing them. Wouldn't that make you more that uncomfortable?