We discussed this question over a group dinner Tuesday night. I opined that none have held up particularly well, mostly because they underestimated the robustness of the modern world and regarded depravity as more of a problem than it has turned out to be.
By stipulation, this universe of books does not include Milton Friedman or pure economics. It does include Russell Kirk, John Flynn, Richard Weaver, Robert Nisbet, and William F. Buckley, among many others. You can nominate grumpy Brits and Europeans who settled in the United States, so yes Road to Serfdom is a contender, even though its main empirical point (socialism leads to loss of political freedom) would seem to be refuted. You can try Albert Jay Nock or Eric Voegelin but Rothbard and Rand do not count as conservatives. Your answer cannot come before the 20th century, so no Federalist Papers and no Tocqueville.
Leave your answer in the comments and also say why. At some point I’ll offer up my pick as well.