My favourite word is 'apothecary'. It just sounds mysterious and shady, just like an apothecary. Plus, it isn't really used a lot. I also like 'convolution' and 'studio' for how they sound.
My least favourite is 'cripple' because it is usually misused as a derogatory term to refer to people using wheelchairs, canes, or other such devices because of a physical disability. Plus, the hard consonant sounds don't make the word roll off the tongue nicely. I'm also on the 'moist' hate bandwagon, preferring to use 'wet' instead.