I don’t know the results yet, but my entries would have to be David Hume (1st prize), Aristotle (2nd) and Bertrand Russell (3rd).
The survey inspired me to use the Phi2Phi app to ask the mirror question: who are the most overrated philosophers? I wanted to keep the survey manageable, so I restricted it to 20th century philosophers who are no longer alive. Hopefully, we can assume that enough time has passed to begin to formulate a preliminary assessment of their worth. Besides, if they are dead they can’t sue...
I made it a multiple choice question, offering some provocative choices, plus a catch all (Other-please specify) category. I also tried to be even-handed between continental and analytical traditions, despite my clear leanings toward the latter. Here were the philosophers I submitted as competitors for the un-prize of most overrated during the last century:
Willard van Orman Quine, best known for his criticism of logical positivism and his push for a “naturalized” philosophy. He denied the existence of a meaningful distinction between values and facts, as well as between analytic and synthetic propositions (take that, Kant).
Ludwig Wittgenstein, had two completely different careers, the “early” Wittgenstein being a champion of the logical positivists (see above), the “late” Wittgenstein arguing that all philosophical problems are just misunderstandings of language (I’m simplifying here).
Michel Foucault, a major exponent of structuralism and post-structuralism, famous for his critiques of historical reason, particularly in his The History of Madness in the Classical Age. And for his debate with Chomsky on justice and power.
Jacques Derrida, famous for being the epitome of the obscure or obfuscating philosopher (ok, ok, that’s a bit of poisoning of the well), a deconstructionist and literary critic. As the Stanford Encyclopedia puts it: “deconstruction is relentless in [the] pursuit [of rendering justice] since justice is impossible to achieve.” Whatever that means.
Bertrand Russell, one of the founders of the modern analytical approach to philosophy, best known for his works on the philosophy of mathematics and his contributions to logic. He was the lead character in the Logicomix.
Martin Heidegger, a major practitioner of the phenomenological and existentialist approaches in philosophy, buddy of the Nazi (the well! what the well!), and a top competitor with Derrida for most obscure philosophical writer of the 20th century. He talked a lot about Being (and Time).
So far I’ve got 38 responses, plus 5 comments with alternative suggestions. If we look at the raw data, the “winner” is most definitely Derrida (15 votes). The rest are surprisingly scattered, with few votes each: Foucault (6 entries), Quine and Heidegger (4), Wittgenstein (3), and Russell (2). 
If we look at the comments, we find two votes for David Lewis (philosophy of language, metaethics, philosophy of mind; though his most famous contributions are in metaphysics, including his modal realism, about which Leonard has recently written). One person voted for Ayn Rand, whom I do not consider a philosopher, and who therefore shall be henceforth ignored. Another voted for Karl Popper, the philosopher of science who gave us the idea of falsifiability, and one commenter said that “Russell is the most underrated of the list,” which I took to be an anti-vote, unless the comment was meant ironically.
Now, the Phi2Phi app also allows the filtering of the data according to a number of criteria to see what certain subgroups of users think. Given the limited number of responses thus far, there is only so much data manipulation I’m willing to do, but what the heck, this is a blog, not a peer reviewed journal (though some of our readers occasionally make the mistake of confusing the two).
The most obvious filtering to be done is keeping only responses from people who are academic philosophers (both graduate students and faculty), to see if a clearer picture emerges once the field is left to the pros. Derrida still “wins,” but he is now followed closely by Foucault and then by Heidegger. That is, the continental entries in the list fared much worse than their analytical counterparts (Wittgenstein counts as both, but still). Of course, this could simply reflect continental philosophers’ antipathy for surveys (they are attempts to scientify people’s thoughts, after all!), or for apps, or for Apple devices.
Phi2Phi also allows one to filter by categories of interest. Applying the “continental” filter (i.e., leaving the field to self-professed continentalists) surprisingly yields Heidegger as the most overrated philosopher of the 20th century!  He was followed by Wittgenstein (also somewhat surprisingly) and Russell (perfectly predictable).
There is no “analytical” filter on the app, so I used “language + logic + science” (all favorite analytical themes) instead. The winner, once again, was Derrida, followed by Heidegger, with no votes at all for Russell.
One more twist. I wondered what users who listed science as their academic field thought of these people. There were no answers at all logged into the system.
So, let’s open it up to discussion, readers. Who do you think are the most overrated philosophers of the 20th century? And if you’d like to extend the survey to those still living, well, I’ve got a couple of suggestions there too...
 By this time I can see some eyes rolling around. Massimo, do you really think this is a scientific survey? A representative sample? No, of course I don’t. But it’s fun to think about what others are thinking, which is the whole point of the Phi2Phi app. Relax, this isn’t science. Or philosophy, really.
 However, the number of votes is now pretty small, so this could simply be the result of a stochastic fluctuation.
Reprinted from Rationally Speaking, January 11, 2013