Here are some portions of The Maverick Philsopher's post on the question, which was recently polled by the BBC:
I would give top honors to Plato.
Russell doesn't come close to greatness. As Feser remarks, his writings on ethics and religion are "drivel," which may be harsh but is in the vicinity of the truth. His work in logic, epistemology, and metaphysics, though brilliant and influential, is largely derivative from Frege and Hume. On the topic of existence, I believe he is just dead wrong. Surely, a philosopher who is wrong on fundamental questions cannot be called great.
Compared to earlier centuries, the 19th century was not particularly good, and the 20th was a disaster. A century in which Wittgenstein and Heidegger count as great is an impoverished one indeed. Wittgenstein, as J. N. Findlay once remarked, took every wrong turn a philosopher can take. Historically, he was an ignoramus, and his conception of philosophy miserable: the great problems of philosophy are for him nothing more than conceptual tangles that result from "the bewitchment of our understanding by language" (die Verhexung unseres Verstandes durch die Sprache).
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