Ranking is, using Rand's terminology, teleological measurement. It helps keep one's mind limber. One ranking I've spent maybe too much time thinking about is the following:
Babe Ruth
Willie Mays
Ted Williams
Ty Cobb
Honus Wagner
Mickey Mantle
Hank Aaron
Barry Bonds (pre-1999)
Mike Schmidt
Lou Gehrig
Rogers Hornsby
Stan Musial
Rickey Henderson
Joe DiMaggio
Yogi Berra
Johnny Bench
Joe Morgan
Albert Pujols
Ken Griffey, Jr.
Pete Rose
(Where Mike Trout fits in here yet is not yet determined, but I assume it is probably in the top five. And pitchers seem to require a separate ranking.)
Or there's this ranking:
Ludwig van Beethoven
Johann Sebastian Bach
Wolfy Mozart
Gustav Mahler
Dmitri Shostakovich
Franz Schubert
Anton Bruckner
Jean Sibelius
Ralph Vaughan Williams
Joseph Haydn
Johannes Brahms
Bela Bartok
Igor Stravinsky
Pyotr Tchaikovsky
Frederic Chopin
Claude Debussy
G. F. Handel
Robert Schumann
Gyorgy Ligeti
(I don't know where to rank opera composers (e.g., Wagner) or atonal composers (e.g. Schoenberg.))
But a (teleologically) more important ranking would be one like this (more or less aggregated from numerous sources):
Aristotle
Immanuel Kant
Plato
David Hume
Rene Descartes
G. W. F. Hegel
Ludwig Wittgenstein
G. W. Leibniz
Baruch Spinoza
Friedrich Nietzsche
John Locke
Thomas Aquinas
Gottlob Frege
Karl Marx
Thomas Hobbes
J. S. Mill
Bertrand Russell
Martin Heidegger
Michel Foucault
Soren Kierkegaard
Arthur Schopenhauer
Edmund Husserl
C. S. Peirce
John Dewey
W. V. O. Quine
Augustine
Plotinus
(For the above aggregation-based ranking I'm not including Ayn Rand, and although I gather that Chrysippus might very well be top-3 material, there are almost no extant works by him. (A parallel case might be Negro Leaguer Oscar Charleston, for whom no good stats/records are available.) Also what about Socrates?)
So, I've studied the ideas of Rand for quite some time, enough to be an expert I'd say. That includes all of the original materials. For the other figures I've relied a bunch (or in the case of Hegel, entirely) on secondary materials. Among the secondary materials on some of the highest-ranked philosophers above, the ones I've found really helpful are the Oxford Handbooks series. I've gone through a half dozen Handbooks so far, and have another half dozen or so in the reading queue somewhere. For the top dozen listed above, there are two (Kant and Locke) for whom Handbooks have not been published yet. I'm just over 3/4 through the Nietzsche one; I put the Leibniz one on pause about 30% of the way through; in the queue are Wittgenstein, 'Descartes and Cartesianism', and Aquinas. That leaves the following which I've gone through, and for which I provide a ranking based on my overall impression of each philosopher's merits (to be explained in due course):
Aristotle
Plato
Hegel
Nietzsche
Leibniz
Hume
Spinoza
Some inchoate remarks: I liken Aristotle to Babe Ruth; he's like the god-status figure of philosophy. [Note: adjustments need to be made for era (as per baseball historian Bill James) in which a philosopher/player flourished.] Plato was the first systematizer and recognized the inherent dignity of philosophical activity over and above mere drives, pleasures, inclinations, opinions, or the 'mundane.' Hegel is something like an abstruse version of a modern-period Aristotle in matters of pure philosophy. (More context/details.) Nietzsche's career was cut tragically short at age 44; how might the world have turned out differently otherwise? (After enough time how would he have avoided a reckoning with Aristotle?) Leibniz is a serious metaphysician (conversant with Aristotle) whose range of learning/expertise might be compared to Aristotle's. Hume is a philosopher of 'common sense' and 'mitigated skepticism' with no pretense to metaphysical speculations. (Blackburn's essay in the Hume Handbook was most useful and one I'd go back to.) Spinoza requires you to accept his definitions if you're going to accept the system he purports to spin from them; his career was also cut too short.
I'd put Rand at least on the level of (shortened-career-)Nietzsche or Hegel; her mostly-lousy polemics only bolster the proposition that she developed so many common sense positions on the strength of first-hand inductions independent of the 'canon/tradition.' Her key strengths are in method, aesthetics, political philosophy, and ethics. She's a plainspoken 'popular philosopher' and as such performs an extremely valuable service to a philosophy-starved public or a newcomer seeking a springboard into the world of 'advanced, technical' philosophy with the aid of her/Peikoff's methodological strictures. It's hard to imagine a more unjustly smeared or dismissed figure in the history of ideas (on the basis of motivations that IMO are quite nakedly political and therefore highly toxic). I see no excuse for the professional (sic) neglect of her aesthetic theory much less her theory of method. She's probably unsurpassed as a political thinker and it's really hard to overstate her contribution to the strongest variants of contemporary libertarian thought (see here for some details). She also had a fine grasp of the importance of philosophy to the flourishing (or lack thereof) of a culture, and as such she (and Peikoff) should be taken seriously as a metaphilosopher. (I can only assume that based on the now-available inductive evidence of the viability of philosophy for children, that she'd be all over that at least as much as anyone else - with, I am sure, some qualifications, e.g., that philosophical activity (even of the most 'speculative' variety) should proceed on an inductive/concretizing and context-keeping basis, and consciously and explicitly so.)
Now, if I were to include in the ranking the other top-half-dozen philosophers for whom I've yet to read an Oxford Handbook, as well as Rand and Socrates, my current impression is that the ranking might turn out roughly as follows:
Aristotle
Plato
Hegel
Rand
Nietzsche
Kant
Leibniz
Aquinas
Locke (probably Rand's equal as a political philosopher?)
Wittgenstein
Socrates
Hume
Descartes
Spinoza
You might tell that I'm not exactly a fan of rationalism as methodology; almost surely that dislike was effectively beaten into me by many hours of Peikoff-course listening. (Also, I'd like to raise the distinct possibility of Hume's being a methodological rationalist while not being a substantive empiricist. He sure seems to be doing some dubious deducing about 'sense impressions' as definitive of all we have access to. As for Cartesian mind-body dualism as I understand it, it reflects a destructive methodology, quite explicitly in reaction to Aristotelian dialectic and (therefore) hylemorphism. Dualisms like mind/body and is/ought seem to suppose that if you can't eliminatively 'reduce' one to the other, they have to be kept separate. But what about mind as, say, supervening on sufficiently complex natural/physical stuff? Or in the case of is/ought, the ought as supervening on sufficiently complex natural facts? (Or suppose that the 'ought' supervening on an 'is' is a species of potentiality supervening on actuality? We wouldn't, after all, have trouble with the 'is' lining up nice and neat with actuality; this leaves us with whether we should conceptualize 'ought' in terms of potentiality, and whether what is and what ought to be are one and the same - that they reach a sort of 'dialectical unity' as it were, instead of some unbridgeable duality or dichotomy - when some species of potentiality is being actualized....) That's a prospect that Parfit quite disappointingly doesn't investigate in On What Matters (well, I still need to get to Volume Three...), instead pursuing some line about non-natural truths that might not even exist in "an ontological sense," whatever that's supposed to mean. I think Aristotle might very well go for a supervenience sort of explanation on such things; incidentally, Hurley mentions supervenience early in Natural Reasons, but she loses me pretty quickly after that. I mean, would you look just at those sentence constructions, much less what's in them? I'm not worthy, I guess.) Also, very high up in my reading queue is the Handbook for Marx, although higher still and to be read very soon is the Handbook on Virtue. Speaking of which, how thoroughly/completely/perfectly will it cover the place of perfectionism in the virtue-ethics tradition? I really, really want ethical philosophers to get this one right. After all, how does one possibly improve upon perfectionism, and Aristotelian/intellectualist perfectionism in particular? I glean an explicitly intellectual-perfectionist strand from Aristotle, Aquinas and Rand, but not so much from all that many of the others ranked above, however much they were pretty much all putting the principle into practice....
(BTW, there's a chapter on order of rank in the Nietzsche Handbook, but the chapter I'd rank the most highly among the book's first 26 chapters is almost surely the one by Jacob Golomb about what Nietzsche meant by 'will to power.' (Oooh, there's an article by him about Nietzsche contra Trump in search results.) Also, I just so happen to have my eye on the newly-published Handbook on Expertise. 1300 pages, eh?)
