Ooh, that's actually really difficult, both being interesting but also icnredibly flawed additional-world constructions. I think it depends on the question of whether just Narnia is real, or whether the full cosmology around Narnia is real. If the latter, I arguably shouldn't want Narnia to be real because in the wider Narnian cosmology, atheists are inherently unicorn murdering mouldy turnip eaters who are condemned eternally to that state after death which doesn't sound ideal. If the former, Narnia is the obvious choice, because Narnians generally don't come over and murder us over here (whereas dark wizards absolutely 100% do murder muggles).
I'll opt for Narnia being real, I think. I actually do like Narnia more as a setting.
Have all your clothes washing and ironing automatically magically done, for the rest of your life, or have a guarantee of good sleep for the rest of your life?