Who's the most interesting philosopher, and why?

[butterburger]

...

[Tongio]

Albert Camus. His books are great, and he lived what he preached.

[El_Jibaro]

Albert Camus. His books are great, and he lived what he preached.

I find Camus deeply compelling, and for me he's the most relatable among those on the existentialist/absurdist axis. He is a wonderful antidote to all the over-intellectual, verbal masturbation out there.

[El_Jibaro]

To answer OP question...hmm, difficult to say but perhaps Spinoza. His metaphysical system is perhaps the most complete, he offers solution to mind/body problem as well as list of propositions derived through deductive reason from set of basic axioms that set out the total scheme of reality in general leading to a naturalized ethical philosophy. The logic of Spinoza really involves no true negation, and all seemingly negative statements are actually the affirmation of something else. Even though people often attribute the phrase "all determination is negation" to Spinoza, there's really no real negativity in Spinoza's logic, only a privation and limitation produced through affirmation.

As for where to start with Spinoza, I would advise beginning with the "Treatise on the Emendation of the Intellect" (fairly compact reading of Spinoza's system though you miss out on a lot of the subtleties and paradoxes of his system) and then start working slowly through the "Ethics". Also, try reading some of the work he is responding to and developing on. He very clearly sees himself working in "Cartesian tradition", so try reading some of Descartes' as he was rather influenced by his ideas (whether he appropriates them or rejects them) also since he tends to be more accessible than Spinoza.

I also like Russel, Sartre, Kierkegaard, Dostoyevsky, Heidegger, Wittgenstein, Camus (as I mentioned in my reply to the gentleman above), Hume, Kant, Merleau-Ponty, Feyerabend, Diogenes, Baudrillard, Adorno, love/hate relationship with Nietzsche, Bergson, etc etc...although I don't have enough time to explain myself with all these choices

[Batavia]

There are so many, if I had to choose one, Nietzsche is on the top of the list, he was certainly one of the most important Philosophers.
I would even go so far as to call him the most important philosopher of the 19th century - he got to the heart of Christianity and the hypocrisy of his fellow men and he was a realist, not a dreamy optimist like Kant.
So he wasn't an optimist, but he was very life-affirming and he was only interested in the truth - as bad as it was.
His life was very hard, but he never let himself be diverted from his path, he knew what it was like to be really lonely.