My favorite philosopher would probably be Ludwig Wittgenstein. Not for his ideas as much (as in fact he practically contradicted himself on every point in his early and later writings ) but his bizzare methods and overall style. He took an extremely unique approach to problems.

As far as least favorite philospher, probably George Berkeley (I don't really even consider him a philosopher ). I'm not sure how he made a living mocking Newton's calculus, while simultaneously spewing half-baked ideas of his own.